Can you transmit variables between worlds?

I want to create a 2d texture of another of my worlds to display on my current world’s wall and use that texture as a portal that players can walk through. I want it to be real time, though so that the player can see other players in that world walking around. Is that possible?

Short answer: No
Longer answer: Yes, but there are many limitations that prevent this from being feasible.
With udon you can technically send data back and forward between a client and a webserver, however, the amount of data you’ll need to send will most likely be way too much.

Additionally, vrchat uses multiple instances/room codes each time a world is spun up. Worlds aren’t persistent either, so if the room becomes empty your portal will break. And lastly, there’s the issue of syncing things.

So, on a technical level, it’d be possible to a degree, but on a practical level the answer is no.

What if I got rid of tracking other players? Could I just use it to extend the world by using a static image of the second world as a portal?