Multiple users at once
I would suggest that Illustrator can open a file on several devices, perhaps 2 or 3 max. and allow a team of designers to work and brainstorm on the same file at the same time as an online service from Adobe.
This can be used for other adobe design programs as well such as Photoshop.
The new Canvases were presented at MAX 2021 , that allow some sort of collaboration on a canvas. Some basic tasks can be done there.
As for the true Ai collaboration, you might want to try Invite to Edit, a big blue button in the top right corner of Ai window. Not yet simultaneous though, and for cloud documents only, obviously.