Added an application to autorun through GNOME Tweaks.
Added an application to autorun through Startup Application.
Combined different ways.
I note that in Fedora Linux one of the above methods works fine. Perhaps this is due to the fact that it uses vanile GNOME. The application via ppa and snapstore also does not work in autorun using Startup Application and GNOME Tweaks. However, the snap version of the application worked fine in the Startup Application using the flameshot %F command. But this was before the previous installation of the operating system and it works every other time.
I'm battleing on a different field with flameshot. A good hint from @Aravisian pointed me to the following page:
later on this page, there are some suggestions to come over the autostart problems (with some delay - I don't understand) but it may be helpful for you to find a solution.