I bought Doom Eternal and Overload (spiritual successor of the 'Descent' franchise) over the cyber-Monday, and still haven't spoiled my uptime by booting Windows play them. With Steam's Proton there's been almost no problems or even obvious performance loss. Smooth 4k 60hz experience for both on Ubuntu 20.04 w/ Geforce 1070. No tricky optimizations or drivers.

The only issues were some audio crackle in Doom before I implemented the forum wisdom to set PulseAudio to 48khz, and, the annoyance that 'tab' stops working in game if I alt-tab out and back.