black rectangular boxes keep appearing as the biome names also appear. it would have been fine if it served as the biome names' background except its just slightly above the crosshair and its infuriating.

tried switching the shadow into false, no dice.

I have the same issue, but text shadow is just shadow on the text to make it look 3d, those boxes are something different...

Were you able to resolve this? I assume it's a mod or resource pack compatibility issue but not sure how it happens.

Try:
Option -> Accessibility Settings -> Text BackGround: Chat