Quite a boring answer from me:

• Steam deck, which gives access to a large subset of PC games and also just about every console up to the PS2/Gamecube/Xbox era plus the Wii via emulation (no jailbreaking required).
• Switch, which gives access to a lot of the best WiiU games as expanded ports plus some spruced up versions of Nintendo's back catalogue.
• PS5, which gives access to most of the best PS3 and PS4 games via PS+.
• Xbox Series S/X, which has backwards compatibility with the Xbox One and Xbox 360 for some (most?) games.

There will be some slight gaps in backwards compatibility/emulator compatibility for some games, but I suspect the biggest remaining gap will be PC games not capable of running on the Steam deck.

Here is what I believe to be the definitive answer for maxing out your library on 4 inputs:

1. Gaming PC/Steam Deck - you'll have access to a sprawling library of games from all generations and can even emulate console exclusive games from previous generations. The reason I'm not recommending an Xbox console on this list is because basically every current gen Xbox One (+ X|S) game is already on PC (as are many OG Xbox and most Xbox 360-era games), GamePass is an option if you wanna play some OG Xbox/360 games legally, and emulation can get you any games that aren't available otherwise. Sony is also making many recent PS5 exclusives available on PC now with more to come.

2. Nintendo Switch - it's got a kick-ass library of exclusives, almost every Wii U game has been ported over (minus like ~8, I think?), they've been remaking/remastering a lot of older games and are reportedly going to go hard on that for the remainder of the Switch's lifespan, and with NSO it has a respectable library of retro Nintendo and Sega Genesis games if you wanna go the legal route.

3. PS4/PS5 - A PS5 would be ideal for maxing out your possible library size, because it can play any PS4 or PS5 game; however, there also aren't a ton of PS5 exclusives at this point in time, PS5 games are being ported over to PC faster than PS4 exclusives, many recent PS5 games are also on PS4, PS4s are cheaper, and the PS4 can be jailbroken. There's a case to be made for getting a PS4 instead.

4. Modded PS3 - Especially if you can track down a phat model with hardware back compact support, you can load up a HDD with games and play the entire PS1, PS2, and PS3 libraries.

With these four, you should be able to play essentially any game ever made. You will have...

Official hardware support for:

• PlayStation
• PlayStation 2
• PlayStation 3
• PlayStation 4 and/or 5
• Nintendo Switch
• PC (Astonishingly huge library)

You will have the (paid) option of legal software support for many of the best games from:

• NES
• SNES
• Sega Genesis
• Game Boy
• Game Boy Color
• Game Boy Advance
• Nintendo 64
• Xbox
• Xbox 360

You will have the capability to emulate anything from Atari 2600 through to some Nintendo Switch, including Xbox, Xbox 360, GameCube, Wii, Wii U, arcade classics, and many, many more.

IMO, this is the best way to max out the 4 ports on your TV. You can also get a PS Vita and mod it for PS Vita + PSP games, and a 3DS modded for 3DS and NDS games. They don't need to be plugged into your TV, so they weren't included on my list of 4, but they are both excellent handheld consoles with great libraries.

1. SteamDeck
2. Switch with NSO
3. Xbox
4. PS5

Now you have literally everything?

Or just skip 2/3/4 and emulate

Me personally, my go-to console at this point is the Steam Deck for its sheer versatility. I've got a dock with an 8Bitdo Ultimate Pro connected so it's more or less plug and play. Since building my first PC in high school, I have a huge Steam library. EmuDeck is also amazing so with the exception of a Series X somehow running emulators, the Steam Deck is the best console for emulation.

I've had an Xbox One S as my 4K blu-ray player and have been digging the backwards compatibility, though there's not enough OG Xbox support. I'm more than likely going to mod an OG Xbox with the Stellar chip/HD mod. I've considered a Series X, but unless it can replace my Nvidia Shield TV as an entertainment box, I'll probably stick to my Onse S. I've also considered a PS5, but their games are coming to PC, albeit delayed, so I don't really feel the need to pick one up.

The PS3 is a special beast as those games are seemingly trapped on the console unless ported (RIP Beenox Spider-Man games). When modded you have the ability to software emulate PS2 games (not as good at the launch PS3 but those things won't last), but for me my TV still has a component connection so my cheat is having a PS2.

Nintendo has one of the most beloved library of games, but the Switch does not support much of said library unfortunately. The Wii U on the other hand had better compatibility especially if you modded in GameCube support which runs natively on the console.

1 - Get Recalbox on a GPi Case 2 and you'll have access to just about every system from before 2000 (including support for commodore and other similar systems). It can handle PSP games as well, but not PS2 or NDS. There are other cases available for a raspberry pi system, but I recommend the GPi Case 2 because you can play it "docked" and handheld. I recommend Recalbox since it already has a lot of support for the GPi case built into it, but if you're tech-savvy you may prefer Lakka for its flexibility. You may be able to get more modern emulators to run on the lakka as well.

2 - Gaming PC with Lakka, Citra, or whatever other emulators you'd like. And unless you're playing a lot of super new games, you don't need anything fancy- you could probably just throw windows 7 on a $100 refurbished business PC and run just about any game from 2010 or earlier, TBH.

3 - Wii or Wii U. I personally find emulation of these (specifically with a wii-mote) to be a bit finicky. If you don't use a Wii, you can substitute your personal console of choice for this one.

4 - Oculus Quest- though I'm not sure if it counts since you aren't connecting to a TV. This isn't the best VR headset but it is the cheapest. It has a good library of standalone games, and for anything else you can use airlink or the virtual desktop to run games off of a VR-ready PC (If you went with one that was beefy for #2). The quest has a lot of modding support through the sidequest. The main concern with this is that you need a phone to set up a Quest when you buy it/after a factory reset. So if Facebook goes under or a meteor hits silicon valley, this could conceivably turn into a fancy paperweight. To my knowledge, nobody has cracked the Quest to skip over this step. If historical preservation is more important to you than money, I would recommend choosing literally any other VR headset because of the setup thing.

I keep the current gen hooked up in the living room and the previous gen in the bedroom.

Older consoles are archived but available.

I'd think:

1. Gaming PC (PC games plus emulation of most systems, including Android and arcades)

2, 3, and 4. Some combination of three systems with large exclusive libraries for which emulation isn't quite there yet or have unique features that make emulation suboptimal (Sega Saturn, Original Xbox, Xbox 360, Wii U, PS3, and PS5 come to mind)

Wii (which naturally includes Gamecube) Switch (with its N64, SNES, and NES emulation) XBox 360 Steam Deck (Steam and all other Pc games, including emulators)

PC, and then whatever the current generation consoles are (assuming they remain just Nintendo, Sony and Microsoft so there are only 3).

Now I have access to every game ever. Mostly on PC due to having a larger back catalogue and through emulation.

If I am not allowed the PC due to it "not being a console" then I will use a modded Xbox instead and still have emulation and the ability to install windows for all those PC games.

Modded PS Vita, since upon modding, its scope of playable games becomes ridiculously high. Native games, PSP and PS1 games supported natively which can be expanded upon modding with homebrews and back ups of official releases you paid for, plenty of emulators for both the Vita and the PSP, wrappers for Android and PC games, as well as ports of game engines, getting released pretty much every week, and OS extensions for forwarding the Vita's screen to another device, making certain bluetooth controllers compatible, fixing/improving the system, and so on and so forth. It's a nice console. :3

I wouldn't buy any consoles, I would build (though you can buy) a really powerful gaming PC to plug up to my 4k TV. I've actually recently done just that and it works amazingly well.

Things to make it a good experience:

1. Make sure you have a 4k TV with HDMI 2.1 for 120hz gaming
2. Configure Windows to bypass the login screen on boot
3. Configure Steam to launch in Big Picture mode on startup
4. Buy an Xbox Controller and the little dongle for it (it works better than just bluetooth)
5. Buy a small wireless keyboard with built in trackpad for the odd occasion you need to use a mouse and keyboard (looking at you EA Play).

With that, you've got the best console ever. Huge backlog of games, games on steep discounts, a machine that has a much better experience outputting to a 4k TV than something like a Steamdeck or a console. I've tried the Steamdeck to a 4k TV and the quality was pretty awful; 720p does not upscale to 4k well at all. And if you wanted to, you could set it up with emulators using retroarch for any games you are missing.

My TVPC specs:

1. Ryzen 7800x
2. 32GB DDR5-6000
3. 2TB NVME SSD
4. RTX 4080
5. Fractal Design Torrent Nano

I picked that case specifically for the huge 180mm fan in the front, the fact it can fit a massive cooler like the Peerless Assassin and the GPU gets fresh air from the bottom. It's not the smallest case, but it stays cool and super quiet.