I reported my issue on Email settings not being saved
The OS was Ubuntu 22.04. And I don’t remember setting any flags anywhere.
I don’t think vmhv’s issue is exactly the same as Sfullak’s, as Dovecot was listed on the Status page for both me and Sfullak. And it’s not the same as for me, as the “Mail server to configure” option resolved the problem for me, but not for vmhv.