@Pondus:
yes, this did it! Thanks for that (quick) help.
But this was not exactly the point. I wanted my FW to be "sharp"
And in all other cases it worked well for years.
And with MS-Firewall in public all worked perfect too.
I stay in private mode now, because I don't want to fiddle with serveral solutions while I can have all in one hand.
And while I can see what avast does with a lot of Apps and Games in the FW Rules-Section I'm pretty sure, it would not be too hard for Avast to handle Veeam EB as well automatically.
And we all know, that the combination of FW, AV AND Backup is the holy grail in terms of End-User Security ( next to intelligent awareness of the Layer 8
)
So, thanks again and have a nice day
Best regards