I can´t manage to open an e-mail attachment directly in Thunderbird.
In the settings of Thunderbird I defined that Excel files should be opened with 'scalc'. Thunderbird refuses to open an Excel attachment.
For now the only way to open the attachment is to download the attachment first. There must be a way to open the attachment directly.
I am a user (no sudo) of Zorin 16 Core.
Question: How did you install Thunderbird. i.e. which source?
I'm thinking if you have Thunderbird from Flatpak or Snap source instead of apt, containerisation may be an issue.
You were right.
I re-installed Thunderbird but this time I did not use a Flatpak or Snap source.
After re-installing I was able to open attachments directly.