I mean, we call 3D as 3D because of 1D and 2D.

No, we call it 3d because there are three physical dimensions we move thru: front/back, side to side, up and.

We experience time linearly, so it’s not included. However time behaving like the three other dimensions isn’t precluded by a single law in physics. Literally everything works backwards just as fine as forwards, except consciousness. We need the cause/effect of linear time to be conscious.

Since they don’t exist in our reality

Think of it like fireworks. There can be multiple in your field of view at once.

Each firework is a universe, with its own unique laws of physics and number of physical dimensions. Multiple are still “real” at the same time, even if they’re incredibly unlikely to interact.

I mean, one of the leading theories on how a universe forms is there’s giant “planes” randomly bumping into each other. On that scale not only are multiple universes “real” we’re all completely inconsequential and incredibly fleeting. Not just as individuals, species or even planets. Entire universes don’t matter.

If you’re interested there’s a lot to learn about with all that stuff, but it honestly doesn’t really matter.