There isn't an MBTI-specific Stack and this one is the closest (and has a MBTI tag) but most of the questions tagged as MBTI are about things like the validity of the system, is it practically useful in the workplace, can it be measured objectively, etc.
Can one ask questions here that would sit "inside" the MBTI system such as:
"my sister/colleague/neighbour/friend/bff/whatever is [xx MBTI type, e.g. INFP]. I have [this problematic situation with my sister/etc]. How should I bring up this subject with an [INFP] or why would an [INFP] do this?
in [whatever the situation is] is this likely to be Ne or Ni function?
what's my type? (followed by a loooong list of information!)
Edited to add: I know that there are a lot of MBTI-forums already, but the problem with the "forum" format is that any answers don't usually have "upvote/downvote" functionality and as such don't have the 'survival of the fittest' (aka total bs answers being posted earlier and being more widely viewed!)
If this isn't "in-scope" for this Stack I would ask that you consider changing the scope as MBTI is a big generator of questions even as you dispute its validity :)