I had this problem last July, and it took quite a while for Tech Support to fix it. I hope I get a faster response this time.
After I run Free up space > System junk in Avast Cleanup Premium (version 21.4 build 11361), iTunes was broken. I could open it, but:
I was prompted to log in to my account, twice, even though I'd already been logged in.
I couldn't change the view (e.g. from Music to Podcasts).
I couldn't even quit iTunes. I had to open the Task Manager and use "end task" to close it.
I've just uninstalled and reinstalled iTunes, and the problem persists. I
Here's the original issues thread:
https://forum.avast.com/index.php?topic=266067.0Apparently the new build of Avast is removing the iTunes files that had been previously been excluded from cleanup to fix the problem before.