V2021.1.4 won't load on MacOS Catalina

If this template helps then use it. If not then just delete and start from scratch.

OS (e.g. Win10): macOS - Catalina
PsychoPy version (e.g. 1.84.x): v2021.1.4
Standard Standalone? (y/n) If not then what?: standalone - dmg file
What are you trying to achieve?:
Trying to run it having installed it

What did you try to make it work?:
it opens as far as displaying a main menu with one option ‘psychopy’ which contains 2 sub options : Hide and Quit

it just sits there then.
Activity monitor shows the task PsychoPy running with usually 3 threads (occasional 2 or 5) with the total CPU only changing very occasionally (if I bring the PP window to the forreground)

Any sugestions to get this working would be appreciated.

What specifically went wrong when you tried that?: It doesn’t start properly. see above.
Include pasted full error message if possible. “That didn’t work” is not enough information.
No error messages.
NB the Macbook pro is working fine otherwise, though it is old (2012)

So, suddenly after ~15 mins the Browser window finally appeared and it operated fine. I subsequently closed it and reran it and it took about 4 mins to open. Since then, it appears to load fine everytime. There were no other user tasks running and I’d rebooted a few times yesterday and today so I don’t think it was e.g. background updates, though I can’t be sure.