It was not broken,
but Crimson let me sit here with an hopeless outdated Debian, an old Geary which cannot be used for handling a bigger IMAP account and much more problems like this. Also with an outdated flatpak which gives me problems with outdated and no more maintained runtimes of Gnome/Plasma etc.
With Mobian all these problems are gone, I have a maintained Geary, Evolution, Flare and all the other things I need for a phone used as an daily driver. Also receiving and making calls with an configured SIP account are working absolutely flawlessly. Also Geary does what it should and runs stable and usable with my corporate IMAP account
Therefore I am happy with it and for the first time the phone is usable (like in PureOS) AND all the maintained and actual packages from Debian could be used
For me Byzantinum can come or not now. I finally found an alternative with an maintained and up-to-date Debian and I am happy with it.