I’d say that’s your main issue. Mint isn’t really optimised for gaming, as it uses an old and non-gaming optimised kernel, and most packages in general are pretty old. When it comes to Linux and gaming, the #1 rule is to try to get the latest kernel and graphics drivers. You could install a more recent and optimised kernel on Mint, but if you do that you risk breaking things, which may especially happen when you do your next OS upgrade. So I’d recommend switching to either a gaming-optimised distro such as Bazzite, or a distro which has the latest packages and is optimised for performance, such as CachyOS (although I wouldn’t recommend it if you’re still very new to Linux, since it’s based on Arch - if you’re new to Linux then Bazzite would be a better option).
The second issue is - which version of Proton are you using? If you’re using the official Proton, I’d recommend using Proton-GE instead, as it includes a lot of extra patches and tweaks not present in the official Proton + uses more up-to-date components like DXVK. You can install Proton-GE easily using ProtonUp-Qt. Once you’ve installed Proton-GE, go to the game’s property in Steam and change the compatibility tool to Proton-GE.