Disinterested third party still works. I have no problem using disinterested to both mean lacks material interest, thus is likely neutral and also not intereste

Disinterested third party still works. I have no problem using disinterested to both mean lacks material interest, thus is likely neutral and also not interested in the subject matter depending on context. The framing of the example sentence sounded to me like it meant the latter. I think disinterested still works to suggest potential neutrality if you frame it properly. This is true of quite a lot of words. Many words have multiple meanings and which meaning applies is signalled by context. "I run for exercise" and "I run this company" and "I will run for (political) office" are all distinct meanings of the word run. It is only confusing if context is not clearly signalled. When I was considering taking up GMing a role playing game, my gaming buddies understood my interest in running (a gaming campaign). My father thought I meant pursuing vigorous exercise. This kind of flexibility of language is normal and healthy. It allows for communicating many things with relatively few words, it allows for nuance, it allows for double entendre and for subtle communication that conveys one thing to one group but not necessarily another. This can be important for subterfuge, or simply for signalling information to a minority of people in public without completely derailing a discussion.