1]
avast passwords has nothing to do with the scan/detection

2]
avast doesn’t store passwords

3]
avast is not just a anti-virus, it is much more.
True anti-virus software hasn’t been around for at least 15(!) years.

4]
There are many ways to check if a password is weak or not.
The length is just one of them.

5]
If avast says your password is weak it is time for you to change it to a strong password.