Thank you for paying attention to this topic.
I see what's going on now ...
I was logged into my "lunker" forum account in both Firefox and Safari, and I couldn't see the forums for the new instruments.
When I opened the forum in Edge, I wasn't logged into my forum account yet, and I could see the new forums. But as soon as I logged into my forum account, the new forums disappeared. And if I log out of the forum in Firefox or Safari, the forums for the new instruments become visible.
If I log out of the forum, and then go inside one of the KORG MS-20 child forums, I get this message when I try to log into my account from inside the child forum:
"The topic or board you are looking for appears to be either missing or off limits to you."
So it appears that somehow the new forums are off limits to my account. I don't think I have done anything to get on Arturia's black list (and why would they hide only the new forums from me???), so I suspect that the new forums are not open to all accounts yet. Were they only open to beta testers and super-users during the pre-release period, and they just need to be activated for all users? Just guessing ...
I recall this same problem with the "3 Filters FX" and "3 Preamps" packages. It took several weeks for their forums to show up after they were released. I thought it was just an oversight that Arturia didn't create those forums right away, but now it seems that maybe they were there and I just didn't have access to see them right away.