Only if you accept Russia's description of where the border is. The border as defined by every other country in the entire world says Ukraine is still in their own territory.

There have been some Ukrainian sympathisers setting off bombs/shooting down aircraft/etc inside Russian territory - but those aren't Ukranian soldiers and they're pretty generally just a few random/nonconsequential attacks and don't show any signs of being linked to any "Operation". The front line of the battlefield is nowhere near the border.

Well, here's some footage with a shot down C&C plane. I mean it still could be not Wagner, but it would be an awful coincidence.

I mean we still don't know shit beyond the fact that Ukraine is holding strong and slowly reclaiming territory. The thing about this story is that it shows that the Russians are divided, and that's not a picture you want to show in a war, especially to your people. These events are costing the Russians dearly in one way or another.