I don't see a problem here. It appears you and your system were essentially doing nothing, except running this scan. So it makes sense the security scans - especially if user initiated - took center stage and dedicated system resources to this high priority task. A thorough scan is, after all, a pretty intense and involved process - checking nearly every file (involving a lot of disk activity), system RAM and the virtual environment and more.
100% CPU utilization is not a fault. It means resources are being fully utilized - that's a good thing.
Now 100% CPU utilization and the system is locked up, that is not good. Or if you started to use the computer for other tasks while scanning, and the security app didn't step back out of the way a bit, that may not be good either.
BTW, there typically is no need for manual scans anyway. Those are mostly for user peace of mind. This is because Defender and most other alternatives are running in real time - constantly evaluating the virtual environment and everything that is coming into the computer as it comes in. I typically only run manual scans when I attach some device to my computer (like a thumb or external drive).
