Linux

1: it’s a cantankerous beast that can smell your fear and lack of computer skills

This can either be true, or not true. It depends on which distro you go with, IMO. There are linux distros specifically designed for new user experiences, and then there are "basic" distros which don't do unnecessary hand-holding for those who are used to the *nix desktop experience.

Making the change has slowly become a more real possibility for me

There has never been a better time to try linux.

I’m pretty much a fairly casual PC-user

If you do light computing, then linux is the best case scenario for you. You won't be changing much about the OS, so not much can go wrong. I installed linux for my 65 year old mother 12 years ago or so, and it's never had an issue. So frankly, I wouldn't worry too much about it.

Will my ability to play games be significantly affected compared to Windows?

As with all things when it comes to linux, it depends. Some of my favorite games have anti-cheat which has no linux client, so therefore even if you can get the game to work in theory, it won't function because no anti-cheat.

If a program has no Linux version, is it unusable, or are there workarounds?

You would be hard pressed to find something which is windows only these days, but even if you do there are virtualization options like WINE or bottles which simulate a windows environment for the application and force it to run under linux anyways.

Can Linux run programs that rely on frameworks like .NET or other Windows-specific libraries?

Sure.

How do OS updates work in Linux? Is there a “Linux Update” program like what Windows has?

Generally, most people use the command line for updating the system itself, but a lot of distributions come with a "Microsoft Store" type application to give you a GUI to update your OS and applications.

How does digital security work on Linux?

Linux works off a multi-user environment which lends security to the OS. You have a root user, which is your super administrative user, and then normal user accounts which can be added as "administrators" which can then run commands and edit files/settings which are reserved for administrative accounts.

Is it more vulnerable due to being open source?

The security is stronger because we know what's in it. Security through obscurity is generally frowned upon, even by NIST.

Is there integrated antivirus software, or will I have to source that myself?

Generally no, but there still are anti-virus available, like ClamWin.

Are GPU drivers reliable on Linux?

My heart says yes, but my fingers won't let me type it.

Can Linux (in the case of a misconfiguration or serious failure) potentially damage hardware?

It's technically possible, but you would have to meet a laundry list of conditions for that to happen.

And also, what distro might be best for me?

New users seem to really like Mint. But it's exceptionally easy to test different distributions, even directly under Windows using Hyper-V. Test a few out and see if you like em.