Could be small or big.
My answer has always been that, Linux can't handle everything I'd ask out of it that I normally can with Windows. I know the games issue has been progressing far from the days when that used to have been an archaic flaw with Linux for the longest time. Games might not be the issue except for some concerns I have for some games.
I was taking some time a few moments ago, to check if a program called Firestorm Viewer would work on Linux Mint which could've been my distro of choice. And the description written on the linux page described exactly the kind of concerns I'd have for compatibility and usability from going Windows to Linux.
They said that their viewer was tested and designed to function mostly with Ubuntu and while it could work with other distros, it's not to be expected to be smooth.
That's the kind of sentiment and concern I have always had with Linux if I were to go from Windows to it. There are programs and tools on Windows that I have that are used for specific purposes and I know they will not function on Linux. Furthermore, incase anything breaks down, any and all solutions would only be applicable to that thing that would be far easier to solve than just being SOL if I was on Linux.
It is something as a user that I just can't simply afford to deal with on a regular basis if I made the switch.
So while I may not have too much of an issue running games, I won't have too much of an issue using alternatives, I won't have to deal with the Windows ecosystem .etc I will just be running into other walls that would simply make me second guess my decision and make me regret switching to the point where I would dip back into Windows in a hurry.
I have terabytes of games, shit internet and no patience for things that don't just work immediately. I can only tolerated windows because I've already fixed it and I don't have to keep fixing it anymore.
Who knows what will happen with my next gaming laptop though, if it's fresh and empty I won't have that excuse, although there is always 'cbf' to fall back on.
I use Endeavour and it's near flawless because all the drivers are imstalled, Steam knows when to use Proton, Heroic Launcher handles everything else. 6TB+ of games. All run. When they don't it's because of Epic Games' login requirement. No crashes. No launch errors.
Basically, there's no excuse for incompatibility any more. One exception may be some online multiplayer games with kernel level anticheat that's not supported by Proton. But I don't play those so idk
Compatibility my only concerns are modded games afaik. Forza I think has issues but I'm pretty sick of forza, anyway, fh5 gave me a ton of grief.
It's literally redownloading everything. My internet is likely slower than the moon. Im not touching it without needing to start from scratch anyway, because it'll knock my internet out for like a month.
You can back up your games using steam's game transfer tool to another drive, then attaching that drive to the new install :)
It's even designed for people with data caps. (Since most compatibility is through Proton it shouldn't have any difference in the actual game files)
My data cap isn't even the problem, hitting it is lmao.
Didn't know the same game files worked though, good to know.