Assuming your username on the system is lubuntu, then the /media/lubuntu/ path should be exposed via the removable-media interface of snapd - and the thunderbird snap does list this interface - but it is just not auto-connected. So it may just work if you then run:
Assuming your username on the system is lubuntu, then the /media/lubuntu/ path should be exposed via the removable-media interface of snapd - and the thunderbird snap does list this interface - but it is just not auto-connected. So it may just work if you then run:
sudo snap connect thunderbird: removable- media