Delete broken user accounts on FP OpenOS 7.1.2

I see no way to delete user accounts from attempts to login to apps
I cannot get into some applications because of this.
Phone is rooted, adb is available.
Where is the account manager data base in the file system ?
How can I list the content and distinguish good and bad entries ?
How can I delete bad entries ?
all hints from the search engines do not apply .

Wasn’t it, that each application creates a user on installation? How about creating a backup of the app in question, uninstalling the application and reinstalling from backup?

Yes each application creates a user on installation, and I have seen about 30 users in some directory. I have 45 apps, will not grow anymore with this mess. Actually I need 6 users for calendar, contacts, nextcloud data, email, and some Mapping service with Openstreetmap .
I have done this before, but this database survives
reset of dalvik cache,
reset of app storage,
deletion and reinstallation of individual apps,
all updates of OS
Started in Nov 17 with the actual FP2 OOS, now 7.1.2.
As the file system is new to me, I know Linux since 1997, (FHS about 2005)
there is little information about.
My F-Phone 2 is almost google free and shall stay that way. Battery lasts three days. (would be two, if nextcloud app worked.) ( I use the search engine)
I think it is intentional that this database has no menu Item for flushing out historic accounts and failed accounts, e.g. with wrong password., e.g. which have not been used from 3 month.

Yes, the user database will certainly survive an OS upgrade, but I could imagine that it doesn’t survive a fresh install from OS, especially the “manual switcher” one: