Recently Trackmania 2020 released on Steam and it required the bleeding-edge build of Proton Experimental. This is how you go about enabling it.
1. Search for experimental.
2. Select and install Proton Experimental.
3. Right click Proton Experimental and select properties.
4. Select BETAS then bleeding-edge from the dropdown menu.
5. Missing Ubisoft Connect? Install Steamworks Common Redistributables and relaunch the game.