Would have really, as has been mentioned in the above posts, opened a new thread due to my most recent post above. But unfortunately, I make a concluding post here when partly positive effects have been achieved.
Tested the following in an attempt to fix the problems with Tutanota after ClearLinux crashed as per post above.
Downloaded a new AppImage by Tutanota, and removed the old one. Unfortunately without logging out, which probably caused some problems with the connection, since it now does not get in touch with the Tutanota server. May probably contact Tutanota about this. But now at least the app started.
Might also mention that I use an AppImage from Tutanota, since the installation under software is outdated and therefore no longer supported. So not possible to use!