Start new Windows session. Start Thunderbird and works OK. Shut Thunderbird down and try to re-start during same Windows session and it will not launch. Reboot Windows and try to start Thunderbird and works OK. Alternatively, going into Task Manager there will be a number of Thunderbird processes running. If I manually end them all (while Thunderbird is NOT active) then I can restart as normal too. This all began with 124.0 Beta 1. Never had the issue prior.

Also, Thunderbird crashes if restarting within the app. By this I mean clicking the X it appears to close (excepting those persistent processes running) but "Restart Thunderbird" such as to launch Troubleshooting mode or from the "Restart to update Thunderbird" config crashes the app with 100% consistency.