run this 1 line:

env WINEPREFIX=~/.local/share/Steam/steamapps/compatdata/16700/pfx winecfg
# if your steam location is different, change the path

This will open a window. Cancel the "mono installer" dialog.
In the window, go to the graphics tab and check the box for the "mouse capture" and "create a virtual desktop" with your screen resolution. On my system, this resulted in a blinking blue screen at startup, but enabled "Alt-Tab" functionality.

Start the game with Proton 5.0 and close it. Then, use the following command after you installed "protontricks" for your distribution:

protontricks 16700 directplay

After directplay is installed, you can change back to the default Proton version. I got permission errors, when trying to install directplay with higher Proton versions.