If Avast is not running on startup, you can try this troubleshooting methods:
Make sure that you have enabled the start avast antivirus at startup settings.
Always make sure it is on set to run on startup in windows.
Uninstalling Avast and then reinstalling it again
Try disabling any unnecessary programs and see if that resolves the issue

Read More:- https://cleanersuite.com/avast-background-service-not-running-windows/