This is still a problem, I read that it has been fixed internally, but it has not been implemented. After today's downtime (21st June 2022), I and I presume a lot of other people still cannot enter this cave to complete a part of the Halas timeline, because we get an error message that we need Sentinel's Fate to access that zone.
You presume right since today was a downtime and not a patch. Next patch should be due next week. And what was wrong with updating the existing thread instead of starting a new one?