Ripped this off from another guy named Julek.
Thread found here:
This worked for me, no guarantee that it will work for others.
Hi all,
I had exactly the same issue, impossible to create any game but I found the solution.
This is coming from the Windows Firewall.
Go to Window Security → Firewall & Network protection → Allow an app through firewall.
Once in “Allow an app through firewall”, select “Change settings” then click on “Allow another app”.
This will open a new menu, click on Browse and look for the D2R.exe file should be in “C:\Program Files (x86)\Diablo II Resurrected”, then click on “Add”.
Diablo 2 R will show in the list of “Allowed app and features”, make sure that Public and Private options are ticked and click on Ok.
You should now be able to create a game.
That’s what I did and now I can play the game properly.
Hope this helps.