Do you get the feeling you’re infected?

If you suspect you may be infected with malware, you could run the built-in Windows Defender app. If you think Defender has been compromised, is out of date and updates might be getting blocked by malware, you can always hire a bigger gun.

Incidentally, if you do suspect major malware on a PC, you should disconnect it from the internet and any unnecessary devices right away. Then you can find and install Microsoft’s Safety Scanner using a separate PC and save the executable on a thumb drive to copy it to the suspect PC. Then just run it. The copy of Microsoft Safety Scanner that you download is only valid for 10 days, because you’ll always need a new version anytime you need this type of deep scan.

If you'd like to try one by another brand, most antivirus brands have a stand-alone, on-demand, no install app you can get. I hear good things about Sophos Scan & Clean.