In terms of single-player games, the figure is more like 85%. You can probably get an additional 5% to work with various levels of tweaking, but compatibility is remarkably good these days. Many games perform better on Linux than they do on Windows (Borderlands, Overwatch), while others give you a chance to have a flawless experience with games that are pretty busted on modern Windows (Diablo 2, Fallout: New Vegas). As another commenter mentioned, the big issue is with anti-cheat: any game implementing EAC will outright not work, full stop. That makes it about a 50/50 chance that multiplayer titles will work on Linux, with some unfortunate casualties like Rainbow Six Siege and Halo MCC's online multiplayer.
With that being said, I truly and honestly believe Linux is the way to go if you're not into multiplayer. Valve's commitment to Linux is nothing short of herculean, and it's heartwarming to see them give back to the open source community in such a remarkable way. If it weren't for Proton (and DXVK), I'd still be using Windows on my main computer, which made development hell. Now, I feel comfortable moving to a system where I can enjoy Overwatch, Titanfall and Team Fortress on a regular basis without dual-booting.
With that being said, I truly and honestly believe Linux is the way to go if you're not into multiplayer. Valve's commitment to Linux is nothing short of herculean, and it's heartwarming to see them give back to the open source community in such a remarkable way. If it weren't for Proton (and DXVK), I'd still be using Windows on my main computer, which made development hell. Now, I feel comfortable moving to a system where I can enjoy Overwatch, Titanfall and Team Fortress on a regular basis without dual-booting.