I updated my OS today from Windows 10 Home to Windows 11 via Windows Update. My question is, if I can just continue with Avast Free Antivirus as it was installed on Windows 10, or if I have to somehow reinstall or repair my Avast after updating.
You should be able to continue using Avast Free it is was on the system when you updated to win11. It should still function as it should be compatible with win11.
With regard to the wording of your question “if I can just continue with Avast Free Antivirus as it was installed on Windows 10”
Are you saying it isn’t working or isn’t installed after your update to win11 ?
No as it is compatible with win11 it should be good to go.
For your own peace of mind (as you appear to be doing) - just monitor it is checking your internet browsing (Web Shield), email (Mail Shield) and run a scan.