When I attempt to start either version of Sourcetree 4.1.3. or 4.1.5, the process appears to start but I never get to the point where I see the UI appear. I've had to force quit the app to try starting it again.
When I started 4.1.2 after hunting down a copy, it apparently wouldn't do anything until Xcode 13.1 was verified. I saw the alert box with the progress bar appear on screen after starting 4.1.2. The Sourcetree UI did not come up until I patiently waited for the verification process to finish. And then the 4.1.2 UI came up.
I then exited 4.1.2 and started 4.1.5. The UI came up right away, with a dialog saying the app needed to be updated (I didn't capture the dialog and it hasn't come up again).
Sooooooo. Why did Sourcetree have to verify 13.1 first before doing anything else? Is there a dependency on the Xcode embedded dev tools or something?