I’ve read in a few places that there are/could be “white holes” that just spits out matter. Do we know if those are real, or are they just theory right now? Since we don’t know and will never know what goes on in a black hole, I’ve seen theories that they could be worm holes, links to other universes, but most commonly, I’ve heard that white holes where matter is ejected are the most likely to exist. Is there any proof of that?
Do we know if those are real, or are they just theory right now?
They are solutions of certain equations in general relativity.
will never know what goes on in a black hole
That generalization is not advisable.
in a black hole, I’ve seen theories that they could be worm holes
Worm holes are also results of certain equations in GR. However, these are not stable configurations. To make them stable, things that are not likely to exist (exotic matter) would be necessary.
links to other universes
That is VERY speculative.
Is there any proof of that?
No white hole has been observed so far.
Certain things in physics (e.g. black holes) are quite certain. Others are more speculative (e.g. white holes), and may or may not ever be confirmed. It’s hard to tell the difference, unless you have actually studied physics.