As Jeeqbit stated, this is part of the Yokai Watch event, which was a limited time crossover event.
https://na.finalfantasyxiv.com/lodes...tch/vdnaiga67o
It's duration was from Aug 19 2020 to the release of patch 5.4 which was early Dec 2020.
As the event time period has passed, you can not obtain or complete any of the related quests or items.
Any progress you had made in it would have been saved, however by abandoning the quest step you were on would then reset the progress back to before that step. Because of this, if you do not finish all of the steps during any limited time period quest line, you should not abandon the current step you are on in case SE run the event again (at which time you can pick up were you left off)
Possible SE will re-do the event for this year,
maybe.... But if not, you will need to wait until it is re-released to try to complete it during it's time frame.
Oh, and to answer your question on seeing the players all gathered in a spot in the Gold Saucer, but you couldn't see what they werre interacting with, that is likely they are on a step of the current limited time event "Make it Rain" -
https://na.finalfantasyxiv.com/lodes...ign/b1nyoh167i
So, if you want to do that event, best to start now as it ends Aug 11 2021.