If avast is not opening on windows 10, then you can try these troubleshooting tips.
Simply restart your system
Make sure you are using the latest version of avast.
Try to install and reinstall the avast.
If you have any other antivirus, disable them temporarily to resolve the issue.
Contact avast support.

Read More:- https://cleanersuite.com/avast-wont-open-on-windows-10-how-to-fix/