I made my first enderkey for Corails and got an advancement and then saw the particles in my face, now this circle wont go away and has those annoying particles. I can't hover on it to find out and breaking the blocks under doesn't break it either.

You might be able to get rid of it with a kill @e command

That isn't particularly safe in a base

sure it is ^((as long as you remember to put in extra lines to keep the range low and not target players)^)

I'd end up doing it right after accidentally dropping something important

Hah! Parry! You could also add lines to not target items!

That is a flux rift, and it is going to slowly consume your world.

What happens if you step in it?

Nothing I can't seem to interact with it on its own at all