I somehow missed this question. There is an existing asobjc tag, but for reasons I don’t fully understand, Discourse does not allow anyone to use it any more.
Searches of the Discourse forum suggest that a tag becomes inaccessible when topics using it are deleted. Not sure if that is what happened here, but its all I could find.
Go back to #1, select all topics, and assign the new asobjc tag.
BTW, I noticed something unusual. On the all tags page, some tags show up under the “Announcements” category. This might mean those tags were created for that category only. Unless you did that on purpose, you might want to delete those “Announcements” tags, and recreate them available to all categories.
Thanks for noticing this Jim. I don’t recall every doing this, but the asobjc and several other tags were limited to use in the Announcements category. I’ve changed that and now I (and presumably you) can finally assign the asobjc on all topics.
I’ll probably go through all the topics and add the asobjc tag to anything concerned with Foundation.