Malware propgating through usb debugging

Summary: Computer probably had malware. Didn't know. Connected phone to use as midi. Could have turned on usb debugging or usb tethering to see if that helped without knowing what it does as I was an idiot at the time. 4 months or so has passed. No evidence of malware. Should I bother with formatting it? Questions: 1. Should I bother with formatting it? 2. Is it even possible for malware to exist without any indicators? Extra info: Did antivirus scans with Avast, Malwarebytes, Kaspersky and Google Play Protect. None of them found anything.