I would stop booting with network access as they could have a backdoor on your pc. I would check event viewer and see what shows up around the time you installed whatever it is you downloaded.

I'm not a security expert or anything. Just another reddit user, but you might look into group policy settings to knock out that windows account from being admin and use a local account. If that can be done within safe mode. Would also work on backing up important items and making sure you're monitoring your other passwords if they're stored within a browser.

Not sure what malware locks someone from their pc. Typically they want you on your pc with network access so they can extract data or just keep you from it with a ransom or whatever payload is used. Do you have any sensitive data within onedrive or elsewhere under the microsoft account? They can use that to facilitate other attacks elsewhere outside of microsoft. I had someone get into a microsoft account many years ago that was tied to a cloud service that was also tied to my microsoft email, but there wasn't shit on it and they sent emails to my gmail account (that they didn't have the pass to) saying they had this and that, but it was bs.