If you have bookmarked the old forum:
you may never notice that there’s a new one. I know at least one case.
The old forum shows this text which is not very visible:
Howdy, Stranger! We are about to switch to a new forum software. Until then we have removed the registration on this forum.
I believe it would be good to have a very visible banner at the top with something like
This forum is now read only. Join the new forum at https://discourse.processing.org/