Notification sounds do not currently work in the Thunderbird Flatpak.

It looks like the Firefox BaseApp Flatpak has issues loading libcanberra (bug 1662970), which is likely at the root of this issue since the Thunderbird Flatpak is based on Firefox's BaseApp.

There appears to be some activity on that bug recently, so it may be wise to wait for the fix in Firefox's BaseApp Flatpak, as it will likely resolve this issue.

The fix was merged in Flathub [1]

This should be fixed after rebuilding flatpak.

[1] https://github.com/flathub/org.mozilla.firefox.BaseApp/commit/62aea169ed6d4e76ae70ac8052fba426bf65b0b7

(In reply to Emerson Bernier from comment #3)

The fix was merged in Flathub [1]

This should be fixed after rebuilding flatpak.

[1] https://github.com/flathub/org.mozilla.firefox.BaseApp/commit/62aea169ed6d4e76ae70ac8052fba426bf65b0b7

This should also eliminate the need for a separate Thunderbird Base App on Flathub (bug 1825400). I'll go ahead and close both now that my patch has landed.