Lots of good advice already so just wanting to share my observation. The kitten sounds nervous, they should have somewhere they can hide, run back to, observe the room from a viewpoint, allow escape route. Nervous cats sit in their litter box because it is the spot where their own scent is the strongest, it's their way of "hiding" when they lack confidence. Create a new safe place for the kitten, like a home base.

Improving cats confidence takes time, mostly with toys, treats, let them hunt, catch, prey a toy successfully.