Not sure what it was, but the last updates killed my Thunderbird. I am using 'thunderbird-appmenu' on KDE, version 91.2.0-2.
Running in terminal gets me this error;
XPCOMGlueLoad error for file /usr/lib/thunderbird/libxul.so:
libffi.so.7: cannot open shared object file: No such file or directory
Couldn't load XPCOM
Edit to add, happened on both my systems, reboot after updates, causes Thunderbird to crash on start.
Users be warned.