Experience: I have a bit of experience with Linux. I started around 2008, distro-hopped weekly, decided on Debian until around 2011, when I switched to Windows as I started getting interested in gaming. Tried switching back around 2015, this time using Arch Linux for about a month, but had some bad experiences with gaming and switched back to Windows. I have had a Debian and Arch VM in Virtual Box since then for testing different applications and a more coherent environment to work with servers.
Understanding: Which brings me to now, I am really interested in using Linux for gaming, I know there is Proton from Valve and that they have been really pushing Linux gaming forward with it.
Thoughts: I have been contemplating dual booting by installing Debian to an SSD and simply using the UEFI boot menu to choose instead of having to install to the EFI of Windows.
I guess, I should just do it, as it won't affect my Windows installation, and I could test different games and if all works well, move over. This would also allow me to try different distributions, though my heart is for Debian, I even like Debian Unstable.
Note: I am sorry for the wall of text, I am just kind of anxious I guess.
I switched last year and kind of was in a similar spot to you - I had tried to switch in the past but something didn't work so I went back to windows. But that last attempt has stuck. So I'd just do it. Proton is in an amazing state, old games and even most new singleplayer games will work - some modern multiplayer games with anticheat even work. I'd just check your library on protondb (you can sign in to see your library), see what doesn't work, if you care about it, or if there are workarounds.
What I also did is make a list of stuff that doesn't work and then find alternatives or workarounds. If some games don't work, you can hold off on switching, check protondb occasionally and see if something changes. But if it's all good, I'd just make the jump.
Anti-Cheat was one of the major things that pushed me back to Windows for gaming. They often aren't compatible, invalidating the newly proton-compatible game
Yeah that's big area that's shaky with proton. Fortunately a few games have been adding support (halo MCC recently did). And for me, I typically only play singleplayer games - the most modern multiplayer game I play is titanfall 2 which works great on Linux.
But for someone who does play those games, I can see how the lack of them can be a huge obstacle.
I like your idea of making a list. If all goes well I might just move over, and keep Windows on a small disk for any outliers.
Yeah keeping windows on a separate disk is a good idea. I was going to do too that but I fucked up a dd command and somehow broke the original installation... So I just said fuck it and went full Linux.
I believe Protondb has the option to sign in with your Steam account, and show you the status of everything in your library.