The forum search is like the gdebi. No results. Didn’t think about installing that way. Haven’t used that method for a .deb pkg since 1998-2000 or so.BTW. The other fail was Chrome beta (I know, I know—I need to sync googles crap to install brave and get my stuff).
Haven’t run firefarce since chrome/chromium showed up. Thunderchicken went by the wayside when Mailspring came out.
and, we learn “no joy”. Missing dependencies or somesuch.
The earlier posts are a bit dated; hopefully your result will be smoother with the current version
but, so far, no one has reported success.
mailspring is an “Electron” app, yes?
Is available as a package from snapcraft.io, yes?
mailspring devs have 2017–2021 snubbed repeated requests to package an AppImage, so…
Seems like you missed the turnoff for UbuntuSlither Road, and wound up here in Thunderchicken Hollow.