Upgrade initially failed. After restart, Software Update indicated I needed to update using Partial Upgrade. After completing this and restarting, it appears that 18.1 Pro was installed.
But now Thunderbird doesn't work.
Software shows that it's installed.
No Start Icon is in the Apps List.
I tried uninstalling and reinstalling. Shows successful.
But no Thunderbird icon.
I tried this solution Thunderbird issues with beta upgrade from Zorin OS 17.3 Pro to 18 Pro - #7 by khcohnen
but it didn't work, the first command fails saying that Thunderbird is not installed.
Appreciate help on fixing.