@vib @icedquinn
Regarding running a game in lower resolution, you can use AMD FSR.
You can enable it easily via Lutris. I'm not sure if it's enabled by default with Proton, but you can install custom Proton builds that definitely have it (I've played with it before, so I know it can be done).
I think it also fixes alt-tabbing issues all by itself, without the need of borderless window mode, or virtual desktop.