Check out protondb to see how your game collection fares on linux. I personally just buy games without checking these days and play on linux but then again I buy older games. Although AAA games also tend to work these days within days of release

It greatly depends on the type of games you play, the vast majority of things I play I just hit play on Steam and that's it. Sure I had to do some setup, i.e. install Proton-GE and set Steam to use it as default for all games, otherwise only some games that Valve tested are available, but all in all it's almost 0 setup.

That being said that's been true for years, so I doubt that if you had a bad experience in 2021 it's going to be much different now. Also you need to realise that not even Windows is out of the box, you had to install drivers and programs, PCs are not consoles and with customisability comes the need to setup. And even though you don't have interest in the technical part of Linux you'll need to learn some of it, just like you did for Windows, and most importantly you'll need to forget the technical parts you know of windows that are different on Linux, that's usually one of the biggest problems I see, people trying to use Linux as if it were Windows and having a bad time.

If you have AMD, for most titles it is as simple as installing a distro and then installing Steam. Then on Steam you will have to enable the compatibility tools, that is it. For Nvidia, setting up the drivers is a bit more finicky, however some distros will preconfigure it for you (such as Nobara, although personally I had a couple issues with this distro, YMMV)

You can search for games status on Linux via ProtonDB. In my experience they just work.

For WoW you might need to look up a YT tutorial to figure out the file paths, but the tldr is you need to install Battle.Net as a Non-Steam game, then launch it through Steam. This is generally a good, easy method for most non-steam titles, just installing it and adding it as a non-steam game.

According to ProtonDB flight sim should work, I habe no personal experience here.

I can't speak for both games you listed, however for WoW - Blizzard games tend to have a good reputation for running on Linux (one of the few good things I like about Blizzard). Sometimes there are a few bugs here and there (OW had a mouse cursor locking problem) but generally they're pretty good.

I have been playing Diablo 3 on Linux for as long as I can remember, even before the massive rise of Linux gaming from the introduction of VKD3D/DXVK/Proton. I know D4 was working in Linux even during the betas, and I've heard StarCraft players who've said the same.

Of course, the system requirements never mention Linux as an officially supported platform, but I can't say I've ever heard of a Blizzard game that doesn't work on Linux (games they develop - games like CoD and originally Destiny 2 where they were only the publisher/launcher host is a different story) so I'd be very surprised if WoW doesn't work.

IIRC Blizzard's anti cheat ("Warden" I believe) is mostly server side which makes things way easier - I mean hell I know a lot of their games even supported Mac OS.

And as the others have linked, for MSFS you can check Proton but I hear the reception is good there too since it's rated as Silver on there.

These days I'm usually just playing the Diablo games from them, and I just use the Bottles app which makes it really easy to play non-Steam games. It even has an option to install the Battle.net client for you, then you login, install the game, and click play - it's super simple.

That was always Gabe's intention with SteamOS when it came out around a decade ago. He has never really liked windows, and definitely never liked the potential for Microsoft to mess with his product. SteamOS was made from the ground up to supplant windows as the primary gamer OS, we are just now witnessing the turning of the tide.

Gabe Newell has been openly critizicing Microsoft for quite some time now and therefore, Valve has been pro Linux for years.

It is not too far fetched that the Steamdeck is their second attempt to make Linux gaming more widespread after the failed "Steamboxes". This and they took the opportunity to make a PC-Switch knock-off when the market was perfectly ready for it.