I am not an FP3 user so I may be wrong … but I think this was a “special” build to restore the Upgrade path for this device … it seems an old build e-1.2-s but with a more recent build date 2025-03-18.
Android 13 (T) is now available for FP3 and you may find that your System Updater will offer you an OTA Android version upgrade quite soon. [1]
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Understandable … are your emails available on murena.io ? As a workaround you might install a second email app, like K-9 Mail or FairEmail.
Clear storage from Mail app will delete your settings (so Mail will have to be set up again) but it will not delete emails which are “still on the server”. Similarly I guess with MVGO your settings and for instance preferences within the app will be deleted … but the app owner’s fundamental data is of course not destroyed so it will be just as you uninstalled and reinstalled the app.
[1] Might be worth trying
Settings > Apps and notifications > See all … apps > 3 dot menu top right > Show system > Updater > Storage & cache > Clear storage