Tested the GoG version I manually added to SteamOS. Did not start with the default option, but works fine when forced to use GE-Proton7-29 (any later versions should also work).

For a full screen experience, use a 16:10 resolution like 1440x900 and scale the resolution down to 1280x800 (-> 89%) by using the build-in resolution scaler of the game. If you use the standard 16:9 resolution of 1280x720, the text will be cut off.