Change the default terminal to iTerm2 then click on the Terminal button.
A dialog appears (There was a problem opening this repository in iTerm2)
The following message in console seems related.
2020-06-28 10:19:32 +0000 (e) Error opening iTerm2 - {
NSAppleScriptErrorAppName = Sourcetree;
NSAppleScriptErrorBriefMessage = "Not authorized to send Apple events to iTerm.";
NSAppleScriptErrorMessage = "Not authorized to send Apple events to iTerm.";
NSAppleScriptErrorNumber = "-1743";
NSAppleScriptErrorRange = "NSRange: {2130, 34}";
}