There seem to be some who really experience an inner voice talking in full-fledged sentences and others with no inner monologue at all. My "mind chatter" as I am writing this down resides somewhere in the middle and mostly fragmented: I kind of "autocomplete" on various levels (grammar, semamtics, form ...) and writing/talking just initiates the process to tie up those loose ends into a (forced) linear fashion. So, when I'm finished with a sentence I see/hear it also for the first time; sometimes in amazement (good and bad).
I find the evolution of human consciousness quite fascinating and the residues of that process still can be seen and infered from individual differences which can differ quite significantly/unexpectedly e.g. ranging from aphantasia to hyperphantasia.
The famous/controversial concept of Jayens' bicameral mentality[0] in which "hearing voices"/"hearing commands" is meant quite literally and only later gets consolidated (through e.g. reinfored cultural practices) to an own inner voice. In a similar vein it is conceivable that there exists a common (not pathological) spectrum between forms of clearly heard (inner) voices to faint unstructured (inner) monologue to no voice/monologue at all. [Of course to a degree open to modulation through different states of consciousness.]