It may be possible that mail synchronization is activated in your Murena account settings on the phone, which overwrites your main password in the mail app with your app password.
I had a similar issue, whose solution (in my case) I have described at Feedback for v2.9 - #84 by Tentos
Current summary if you have 2FA activated on murena.io:
- Update the email app to Version 6.711-2 (it should be listed in App Lounge).
- Deactivate mail synchronization in Murena account settings
- Set the IMAP and SMTP password to the main password of your murena.io account
I assume that your email app is already up-to-date because you have /e/OS 3.0
There is also a related GitLab issue Murena Mail password overwritten by Account manager password does not work with MFA (#8638) · Issues · e / Backlog · GitLab