I don't believe the article is correct that it's used primarily by TERFs to separate trans women and cis women. It has been used that way, but that's not how it was created or how it was used. Its use is kind of rare, but in all the cases I've seen of live usage, it's always been as Twitch intended it: to explicitly include trans women among women.

I don't think it's a great term, since "women" does include trans women, and "womxn" does effectively single them out in other contexts. It doesn't have very wide acceptance, and I appreciate Twitch trying to promote it. I'm sorry they got stuck in the middle of language changes mirroring cultural changes. It wasn't intended negatively and their apology should be accepted.