Hi, let me help you.
Start outside the PC. Check recent sign-in activity on your Microsoft, Google, and email accounts; look for mail forwarding rules or unfamiliar logged-in devices; and confirm nobody added a recovery email or phone number. Then log into your router and make sure the DNS servers weren't changed and that no odd port forwarding or remote management is enabled.
On the PC, open Event Viewer's Security log and look for logon events (4624 and 4625) at times you weren't using it. Check Settings > Apps > Installed apps, sorted by install date, for remote-access tools like AnyDesk, TeamViewer, or Quick Assist that you didn't put there, and confirm Remote Desktop is off under Settings > System > Remote Desktop.