Is there a term for "neutral" in the vein of "pros and cons"

Pros means positive aspects
Cons means positive aspects
____ means neutral aspects

Is there a word to fill that blank?

No. There is not.

However, the terms Pro and Con have come to have slightly different meanings in different contexts. Their origin is from the Latin and in that context means arguments for and against something [https://www.lexico.com/explore/pros-and-cons-origin]. In that context, there is no grammatically equivalent Latin construct now in English.

However, in modern English (particularly American English) "pro" and "con" are used more broadly. As other answers have noted, something which is not "for" or "against" something else (note the generalization beyond logical or rhetorical arguments) might be neutral, non-impactful, trivial, irrelevant, or any number of other things.