I have 112.0b1 (32-bit) Thunderbird on Win10
The notification badge on the taskbar still appears when I read the new mail. Whenever I switch to another page (like Junk, Drafts or Send) the icon disappears.
Same issue on 112.0b2(64-bit) Win 11.
b3 seems to resolve this issue for me.
After one day i can't remember having a notification badge after reading my mails.
Nevermind i literally had this issue 1 minute after posting the answer...
Still happens on 113.0b3
If I click into a second email account and then back to the first, then the badge disappears.
Still happening on 116.0b6. I have also noticed that moving to a different mail box and back will also fix the icon counter.
Same issue Thunderbird 115.1.0