German localized Avast Free Antivirus here, so bear with me for inaccurate namings of UI elements or buttons. Just use human intuition.
I completely uninstalled Avast before I reinstalled it from scratch.
I did not import settings.
The popup window that opens when trying to add apps aka. software to the Do-not-disturb-mode shows multiple duplicate entries, the “finished” does not close the UI, the X on top-right does not close the UI.
But chosen apps are added to the list, which can be seen after …
… the necessary reboot of the PC is done which is needed to get rid off the borked and always-open UI than can not be closed at all.