Correct me if I'm mistaken, but I think it's not listed here because Earth-67 (not Earth-6799, which is the TV Show) was only featured in Into the Spider-Verse and the Spider-Verse Event from the Comics. The Comics are regarded as a different Multiverse, so they are not included in here.
Well, I think that's a bit different. With Joker, there was a clear statement. The producers/showrunners and co of The Gifted and, even more so of Legion, gave only vague statements, so I'll go with the others and say it's a divergent timeline, yes, but has no further connection, and thus is not important for the Multiverse Viewing Order.