The Avast Firewall (I know you haven’t got it installed) and the Network Shied work in conjunction they seem to be intertwined.
Not having the firewall component but still having the network inspector enabled may be the cause of this.
Warning I have recently manually updated Avast Free to version 25.2 and my previous settings to have the two components work in concert went out the window after this manual update. Multiple Network Inspector popups saying it is scanning and no apparent way to stop.
Lots of trial and error later (which unfortunately I didn’t document) I no longer get these popups.