3 B's in a lvl

Depends what you class as good, what subject you intend studying and what subjects the Bs are in. You are unlikely to get into top universities but will get offers for some top 50 universities with those grades.

which top 50's. I have math physics and chem. I will do humanities degree if they take 3B's

what sort of humanities degree?
It's a bit of a leap from maths/physics/chem to humanities - don't you want to continue studying STEM subjects at university?

well after getting 3B's even after working my ass off i dont think STEM is for me. And I hope good unis take 3B's for any humanities subject. Getting a STEM subject is gonna be tougher

Humanities courses take a LOT of self motivation and self study - you're going to need more OOMPH to your interest than "any humanities subject". Especially with STEM A levels your PS is going to need to be a real love letter to your chosen degree subject so leaving it woolly isn't going to cut it.

What humanities subjects do you find interesting? Did you enjoy any in particular at GCSE or maybe like watching documentaries/podcasts about a specific topic?

Humanities courses take a LOT of self motivation and self study - you're going to need more OOMPH to your interest than "any humanities subject". Especially with STEM A levels your PS is going to need to be a real love letter to your chosen degree subject so leaving it woolly isn't going to cut it.

What humanities subjects do you find interesting? Did you enjoy any in particular at GCSE or maybe like watching documentaries/podcasts about a specific topic?

cognitive science

The clue is in the name - its a science, not a humanities subject.
You clearly need to do a great deal more research - and thinking - about what you actually want to study, and why.