I installed Thunderbird version 68.10.0+build1-0ubuntu0.20.04.1 on Ubuntu 20.04LTS with mate-desktop vs. 1.24.0-2 and something weird is happening, I have no icon and entry for Thunderbird in the Brisk Menu Launcher vs 0.6.0.
While I'm able to run Thunderbird via the Terminal, as I said it is quite weird no.
ok, I don't know what happened, but I opened the Edit Menus to see if Thunderbird was under Internet, than it appeared in the menu 
So just to give a little more detail, it happen all the time, at every software I install.
My assumption is, this is due to the cache of my ZFS.
My Ubuntu Desktop turn as VM under Proxmox
The virtual drive is with cache on writeback and inside Ubuntu discard and noatime are enabled.
I hope this might someone else with a similar issue.