I have the same behavior on macOS Monterey. Mailspring 1.9.2
Three Gmail accounts, one gSuite, one IMAP. Counts on each account show and are accurate. No badge icons on dock icon.
Possibly related, I toggled on “Show unread counts for all folders/labels” and it shows the total unread on the combined Inbox, but when I untoggle that setting it still shows the total on the combined Inbox
Same here. I have the same issue on linux. I installed libunity and desktop was already called “Mailspring.desktop” since it was installed from Arch+kde (not deb). I get badges for all the other apps except for mailspring. I really love mailspring and I definitely think it is the best email client but not getting counter badge on icon is a huge showstopper.
This needs to be fixed ASAP.