I only found it because an other helper gave a vague answer and I started to look for the solution. 
I hate it when incomplete help is offered. To me it’s worse than no help but in this case it found the answer you needed. 
Asyn
42
Hi Dave, I haven’t the original link at hand but I reposted it in the German section.
→ https://forum.avast.com/index.php?topic=201769.msg1391479#msg1391479
DavidR
43
Thank you, that will certainly do, as you have given the details/reason in English.
Asyn
44
No problem, have a good weekend. Cheers.
system
45
So this means that there is no true offline installation anymore. Hmmm, too bad, what a pity.
A promising software broken down for… nothing?
Then I’ll have to find another anti-virus solution for my XP-PC. No new user, as I’ll stay with Avira for the other PCs.
DavidR
46
That is obviously your choice, but if you were prepared to allow the XP system to connect during the off-line install, then it should be able to download the required component and go back to being off-line for that system after the restart.