Thanks you very much for your reply. I didn’t know about this interface.
However, the utility is written in Go, thus the home + personal-files interfaces doesn’t work, see Go HomeDir reads /etc/passwd, not $HOME
Also, the tool starts the user’s editor to edit the filter rules for Gmail. This is an issue with strict confinement since it cannot open the default editor set by the user (via EDITOR) neither get the user’s configuration of any editor that might be installed in the snap. Maybe there is also a workaround that I don’t know.