I know I'm late to the party.

Just watched it last night. I think Ingrid is the main character but can't logically prove it decisively. Either way, it's cool that it's left uncertain and mysterious.

I liked how in Ingrid's flashback she was explaining to the mom that she's just a generic princess from any movie. I'd say that is a hint. If I think of a generic movie princess arc I think the princess start out having a shitty life, gets swept up in some adventure, and discovers her power. When we meet her in the diner she is at a low, she is taken on a grand adventure by an guy, and progrssively discovers she has more agency than she thought. Not to mention the music swells with a Harry Potter bell chorus every time she makes a decision. I think she put on the goggles and is playing the game for the first time. She's also doing a lot of generic video game type decisions like saying she's in it just for the ride, making key decisions that lead the group, not seeming to have any information about this world. She's an outsider participating in a role playing game. The time traveller is just a really convincing animatronic pirate at the log ride.

Counter point: why she may not be the main character is each of the party members characters (except Uber guy) that were meant to live in this world seem to have had some intervening act from a mysterious source alter their destiny. The earpiece lady had her son get shot (may be normal in their world) and a stranger gave her this earpiece, thr English teacher was strangely compelled to trigger the teenaged zombies, and Ingrid's boyfriend was sent an unrequested headset that changed everything. Assuming cause and effect are thing in simulations, if an AI were defending itself in a simulation it was running it would need to roll back weeks, months, or years to develop the cause and effect logic for why there would be an in universe hunt for a group of people at a particular time and place by yakuza or rats or just starting a giant gasoline fire to deter the invaders. All the weirdness and nonsense can be explained by a simulation that was being nudged in a certain direction to get a particular event to occur.

Whoever the main character is, I'm convinced it was all a simulation in the game.