Thank you very much it works!
I removed FA's wineprefix from the location stated in the run file. Afterwards I uninstalled supcom from steam and removed wine, wine-mono and winetricks. I also removed everything from the FAF client, including the hidden files in ~/
I followed the guide from @Usling https://forum.faforever.com/topic/12/linux-support/157
and did not have to install winetricks or wine itself manually for supcom to start under Proton 6.3-7.
Afterwards I followed the guide from the wiki.
Last time I forgot to set the launch command in the FAF client, so that was a good hint of you and probably the reason why it did not work in the first place. I think that step is missing in tatsu's video or I missed it.
I am looking forward to play with you guys 