Thanks for the report! I have a fix ready for it and it will be included in the next update, but until then you can install Java and run the .jar file directly.
rightclick on "om101_drm_free.jar" shows Open with "OPENJDK java11 runtime". that doesnt work either. when do you release the update?
That's unfortunate :( I only tested on Ubuntu myself so far. Update should be coming in the next few weeks hopefully once I've gotten around to fixing some other bugs and adding some things players have been asking for.
i found a way. vavle released an update for steam today. now it is possible to add every .exe file into steam and start it with proton. so i downloaded the windows version, added om101.exe into steam and forced it to start with proton 3.7-8. it works!