How many dimensions and universes do we actually have?

4 dimensions (x, y, z, t) and one universe.
If you have evidence of a second one, you should publish it. I'm willing to proofread the paper prior to submission. 😏

This depends greatly on the observers perspective. Viewed in the macro scale from a fixed observer perspective we see a flat, unified, single universe with dimensions expressed in definable quantities. However when viewed from the super-micro "quantum" perspective these terms cease to have meaning as universes and dimensions become infinite and therefor un-quantifiable. As we are only able to model the macro perspective from a human understanding the quantum reality remains accessible only in the imaginary.

There is a theory that alternate universes exist. And when we dream we see ourselves in that alternate universe. I would say many other universes.

The Tibetans say there are at least 3 universes. One of them overlaps ours.

There's at least two, this one and the one in my head.

Infinite

Multiverse or universes is actually a stupid theory.

Universe is a term that encompasses all and that's why it's universal. Time is the only dimension as we keep moving in time all the time. So time travel is just a myth as you need time to travel.

There can be numerous solar systems in the universe with each having its own sun and other planets

So it could be that we could be reborn in another earth which may be more or less advanced than we are. Could be that in space travel they have started getting out of their solar system and visiting others, who we refer to as aliens.

I have no idea, and I am content not knowing while living happily in the one I occupy currently.

I know theres the one in my mind and its got a supermassive black hole in it that consumes everything in sight 🕳️

We have one universe and who knows how many universes and dimensions are out there.

Unknown, although there are lots of theories and speculations.

We'll never know