Thanks for the replies!
Still there is a problem: I made a Dimensional Anchor and placed it near the spawner. But my interface doesn't look like it should be looking. I can't change the range of impact. There are buttons missing. Is this a common problem?
I have a skeleton spawner trap with a world anchor built next to it, but when I leave the chunk, it stops spawning skeletons. Got an idea on how to fix this?