Android

It's a given when you're buying a Redmi or Poco you're basically playing garbage in terms of build quality because their after sales service is a nightmare.

bootloader unlocking

I used to buy Xiaomi products because of the bootloader unlocking, but in practice it is a dystopian nightmare - they have built it so to unlock the bootloader you need a cryptographic signature from them, and they don't give that out all that easily.

You have to sign up for an account with them, use a Windows-only tool to request unlocking, and they have a long wait period (deliberately imposed) to unlock, which sometimes randomly restarts. The wait period is different for different models, and can be weeks.

Their support are unwilling to help unlock immediately even for replacement devices where you want to get up and going quickly - if your device breaks (they are not the most durable phones IMO, as you note) and you get a replacement, you'll have to wait the time again before you can restore a backup of a phone using a custom ROM.

It's possible they have improved, but because of their attitude around what I can do with my own hardware, I've stopped buying Xiaomi gear.

I think one of the ways they save money is using cheap wiring, so it gets hotter than it should. Also, no waterproofing - which is why I no longer have my Xiaomi.

My current Xiaomi 13T would be illegal if the new proposed EU regulation goes through.
I dropped it from about about 40 cm because it fell out of my pocket while sitting in a chair. And it instantly cracked the back glass. It was 4 months old and had never been dropped before.
New EU regulation if it goes through will require the phone can endure a drop of 1½ meter on concrete.

However the HyperOS is very good IMO, Xiaomi used to be criticized a lot for their OS, and I hated MIUI, but although HyperOS looks near identical to MIUI, the feeling when using it is just so much better.
So despite the cracked back, I'm actually pretty happy with it.

Of the 6 xiaomi I have bought for me & family (Note 2, the Note 5 and then Notes 7,8,9,11 IIRC) are all working perfectly well.

The 5 started to have some slight mini-usb connection problems, I cracked 2 screens by misshaps but that's it.

The Honor phones and other cheap ones have lasted approximately 1 year, the (used) samsung fold went on repairs so often it's ridiculous.

Anecdotal evidence ofc.

On a sidenote, after the Note 2 (I don't remember for that one) they were all the note pro, maybe that's why they're holding out?

I've had Poco X3 Pro motherboard eater. 2 in-warranty motherboard replacements, so 3 motherboards dead in total, each lasting on average for 9 months. Quite the lifespan.