Vocabulary import and export let the user pick a file through the normal file chooser. home covers $HOME only, so choosing a path on an external drive under /media or /mnt fails with EACCES — which reads as a bug to the user, since the chooser happily shows the drive.
major browsers and email clients (rationale: the software is designed with security and user privacy in mind)
media (eg, sound, photo, video) editors (rationale: the software is very often used to import/edit/export large files on external devices)
media (eg, sound, photo, video) players/viewers (rationale: the software is very often used to import/preview/playback files on external devices)
media (eg, sound, photo, video) recorders/cameras (rationale: the software is very often used to export/edit files on external devices)
If the application falls into one of the above categories, then the following criteria will also be considered:
the application itself is a mature, well-known application
the snap’s (vetted) publisher is a mature, well-known entity
the snap’s (vetted) publisher is the upstream of the software
if the snap is published by someone other than upstream, the publisher must be vetted and either be an established committer to the upstream or the wider snap ecosystem (eg, an established well-known contributor to the software itself, a member of the snapcrafters group, etc)
if the publisher doesn’t meet these criteria, other options may or may not be considered such as the publisher joining snapcrafters, snapcrafters becoming a collaborator on the snap, auto-connection granted conditional on the snap packaging being accepted upstream, upstream stating they trust the publisher with the packaging, etc.
Thus, -1 from me in this case. You may want to take a look at the FileChooser portal as it may be helpful for this purpose