If you are talking about Windows Defender (or some other equivalent software), asking about changes to Windows, this should be a one-time question. If you tell Windows Defender to accept the program to change Windows settings (dll or registry or whatever) as a permanent and valid change, then it shouldn't bother you again. At least, this is how it is supposed to work.
If in doubt, install Avast by selecting the setup.exe, right click on it, run as Administrator, and install it again.
In any case, after the changes or reinstall (and accepting the changes in Windows Defender if it shows up), reboot again and test. Then please report back.