I faced issues with running installer in windows 11. It was blocked many times and later I downloaded zip and extracted. When I tried to run the application again, microsoft defender kept blocking me. When I chose to run anyway, mcafee realtime scanning quarantined it completely not able to start at all.
I don’t think I’ve had any issues with Windows Defender. Where exactly did you download it from?
If you are indeed running an official build and an anti-malware application is incorrectly classifying ActivityWatch as malware, you need to submit feedback to that anti-malware application and/or learn how to permit incorrectly classified applications to run.