Comment 3 for bug 1881603

In case anyone else hits this problem and is wondering about the root cause, it seems to be because snaps generally can't access data from other applications, so when Thunderbird drops a file into /tmp LibreOffice can't "see" it. This isn't unique to LibreOffice, it causes problems for other snaps as well (e.g. Chromium).

This doesn't happen with the non-snap version of LibreOffice distributed through the Ubuntu archive and available via `apt install`, so switching to that is a workaround, albeit at a lower version (6.4.2 instead of 7.0.2.2).

There are a few Ask Ubuntu posts with additional information and other workarounds:

https://askubuntu.com/questions/1123537/cant-open-file-attachment-with-libreoffice-snap

https://askubuntu.com/questions/1046890/libreoffice-cant-access-tmp-files-in-18-04

https://askubuntu.com/questions/1215305/how-can-i-grant-a-snap-application-access-to-tmp-via-command-line