[MOVIE SPOILER] Need help understanding the link between the ending of the movie and the webseries

Hello! Just finished watching the Backrooms and it's a solid 9/10 for me. It's an atmospheric horror masterpiece. I understood everything regarding what the movie was trying to convey, but the one thing I'm confused about is the role of Async as a whole.

Admittedly, prior to this, I'm not actually familiar with Kane's previous work as a Youtuber/animator. I HAVE, however, actually watched a bit of the Valley View Mall/The Rolling Man videos but didn't know who he was until after I left the theatres. (Kane has an amazing talent as a director!) As I go through reviews and theorists of the movie I find out there are a bit of elements on Kane's webseries and the movie. So I wanted to ask what DID happen to Mary at the end, because I interpreted the ending as Mary was actually not able to leave, but then there are comments from people accustomed to the webseries saying that Mary did leave the Backrooms.

Funnily enough, I was watching the movie with a friend, and I told her that she did not manage to leave, but she brought up about Phil, how he was shown being in IRL, and then I retorted and told her, "what if they all managed to build a facility around surviving the Backrooms lol". But now I don't really know for sure, and would like to know more what Async is, who Phil is, and what would be the most accurate explanation of what happened to Mary at the end.

Thanks in advance for checking my post out :-)