i believe that jane never left project nina and you'll be more convinced after dissecting her escape, because it's sooo suspicious
let's start here. after gaining her powers back, jane wants to go to help her friends in hawkins, just as owens predicted and warned her not to do it yet. brenner doesn't think she's ready and locks her in a nina room.
it looks strangely similar to how jane woke up in the lab simulation. the imagery is pretty straightforward too — we see jane locked in the room with the nina machine behind her. the subtext is basically text. she is stuck in the simulation.
let's revisit the brenner's idea of jane being ready. how does he define "ready"? earlier he says...
jane will be ready when she learns how to fly. and as soon as she flies, brenner and her will leave nina and go to hawkins together to fight one.
something something jane's whole journey in season 5 is leading her to the moment when she... well... flies.
and what happens as soon as she flies?
jane leaves simulation/camazotz/whatever tf it is
project nina is definitely not built only for that one memory they had to show jane. definitely not. because why then brenner says this when jane tries to escape project nina?
which truth? by this point she already learned everything there was to the story of the hawkins lab massacre. what is else there to learn? i hope we soon find out.
how did she spent so much time in the simulation? i believe owens here spells out how they did it
jane won't be the first character who spent 18 months in a coma living in some sort of simulation.
side note!!! i just found it funny that dustin and eddie were putting the final nails in the coffin cranes around the time jane was "escaping" nina. cranes were the prominent imagery in s5 indicating that they are trapped.
now back to this. as soon as jane "leaves" project nina, discrepancies start. as @armencias noticed: one moment there are dead soldiers and fire, another moment they are gone
jane leaves on a funky ass van and the scariest powerful military guy cannot pull the strings and stop 5 teenagers on the first turn? yeah right
but that was just the main meal. here's the dessert. a good one. look how everything turns to orange as soon as she "leaves" nina.
what bugs me is that i don't have a clue what that means. does she never reconnect with mike, will and jonathan? or is she entering their camazotz from project nina meaning that by the point she meets them they are already in camazotz?
hope i'll have my answers soon