Unable to set default mail client - x-scheme-handler in snap .desktop files are ignored

We are working with an ISV who creates an email client. The following is defined in the .desktop file shipped in their snap:

MimeType=text/plain;x-scheme-handler/mailto;x-scheme-handler/theisvsmailclient;

Their mail client calls xdg-mime query default x-scheme-handler/mailto to see if it’s the default mail client / change that setting. They are not able to call that from within the Snap of their application. Not being able to call xdg-mime means the app won’t be able to tell if it’s the default mail client or change that setting.

sounds like just another incarnation of:

Yes. See: