What is going on outside our expanding Universe

Do astronomers have atleast a slightest idea about that?

You obviously don't recognise it, but your question makes exactly the same mistake as the flat-earthers used to do when they worried about falling off the edge of the world (only with one more dimension). There isn't any 'outside the universe'. The universe, whether infinite or finite but unbounded, is all there is. I know it seems strange and counter-intuitive, but a lot of cosmology is like that.

There is no "outside" of our universe. It is all that is and isn't there. When someone says that the universe is expanding, most people assume it is expanding into something, like a balloon. Try to think of it more like the very fabric of space and time is being stretched.

There is nothing "outside" the Universe.

There is nothing "North" of the North Pole.

Astronomers and Astronauts both have more to tell.

Nothing. There is no outside.
We might as well ask: "What's going on in the future right now?"
Spacetime is expanding. Not just space

No, they don't. (Yet.)