The problem seems to be that during the upgrade to 18 Pro Thunderbird was replaced by the Snap package. The profile data was located in ~/.thunderbird before (and still is) but the new Snap version is looking in ~/snap/thunderbird/common/.thunderbird for the profiles. I heard that copying the folder to the new location would fix the problem, but I chose another way. I removed the Snap package and installed the .deb version instead and all my data is back again.
-
Remove the Snap Version
sudo snap remove --purge thunderbird -
Add Mozilla PPA:
sudo add-apt-repository ppa:mozillateam/ppa -
Define APT priority
echo 'Package: *
Pin: release o=LP-PPA-mozillateam
Pin-Priority: 1001
' | sudo tee /etc/apt/preferences.d/mozilla-firefox
- Install Thunderbird as deb:
sudo apt update
sudo apt install thunderbird