As first step to slowly migrate away from Google/Microsoft, I would like to have an the calendar and contacts apps with bi-directional synchronization to/from murena.io;
I still need the standard Android for access to the company resources.
I already have an “e.email” account.
Is it possible to simply use APK files from some /e/OS device?
Well, calendar changes entered in the murena.io cloud are synchronized to the phone, but not into the other direction. Is this normal behavior of DAVx5?
If yes, then I still need the /e/OS apps for contacts/calendar …
No you do not need /e/OS apps. In the past I used to sync my /e/ contacts and calendar to other ROMs using DAVx5. Syncing worked both ways. Any changes made in the default apps (Contacts and Calendar or Etar) synced back to the cloud. All of the devices were okay.
Granted that was a long time ago but I doubt anything has changed in that regard. At least I hope not.
Far as I know text messages are a carrier/local thing. No connection to Murena.
For that you would probably use a SMS backup tool like SMS Import / Export or SMS Backup & Restore (App Lounge or Aurora Store).
Makes sense with text messages.
Regarding Notes I’ve tried to use Nextcloud Notes but they require Nextcloud files which I do not see on F-Droid. Could you please advise how did you make it working with Nextcloud Notes for Murena account?