Thanks for the suggestions. I have tried adding sage (pointing to mintty.exe in <user dir>\AppData\SageMath9.3\Local\runtime\bin and the whole directory SageMath9.3) to exclusions, but to no avail. I also tried disabling Windows Defender (Real time & Cloud delivered & Tamper protections, all 3 off) to see if sage runs, but this too does not help.
I see in task manager that while the prompt "Please wait while the Sage Jupyter Notebook server starts..." is shown, registry, python3, and Microsoft OneDrive comes up. And then everything closes.
Is there any logfile that stores possible errors?
On a different note, i also tried to install sage in lubuntu (ubuntu with lxde desktop) where the prompt interface works, but i can't bring up a plot of sin(x). But i think it may be more appropriate to open a different question along with the relevant errors.