How do I know if my MacBook Air was compromised prior to Monterey 12.5.1 software update

My MacBook Air was playing odd music and doing other strange things last night including desktop picture changed which is another question I posted earlier. OS was Monterey 12.5. When I checked for updates it said none were available but 12.5.1 was out there. I reinstalled OS over night and this AM Monterey 12.5.1 is what the OS is but my computer is still doing odd things like if I restart it messages and safari windows are both coming up even though they are not selected to open on start up in options. Avast says no issues found but I'm not thrilled with Avast. How can I tell if I'm really affected and how would I fix it?