Is there a prefix to denote neutrality?

You can go with quasi-

M-W.com

resembling in some degree

Lexico

1.1Being partly or almost.

This is demonstrated well by your own example of social

quasi-social

(Of an activity or relationship) having some but not all of the features that would identify it as genuinely social; having a social aspect but with some other purpose or motivation; Zoology (especially with reference to insects and spiders) exhibiting some of the characteristics of social organization, especially cooperative brood care.

This would work for many examples (quasi-literate, quasi-real, quasi-federalist), but it wouldn't work so well with gnostic because capital-G Gnostic has such a specific meaning. Quasi-Gnostic has the meaning, resembling or having some parts of Gnosticism. But I'm not sure there is a need to need to distinguish between the literal meaning of gnostic and agnostic in any event. These usages are uncommon and likely to be confused if you try to find a middle ground. Either you have knowledge, or you do not. In real world usages, agnostic is already a midway point between theist and atheist.

Prefixes that denote the concept of “both” — rather than neutrality — are sometimes used in situations similar to that in the poster’s example. In addition to “bi-” (which is more strongly associated with the number two) these include:

amphi-

Greek, meaning 'both' or 'on both sides'. Chambers

ambi-

Latin, from ambo both. Chambers

The are relatively few examples, many of which are technical or scientific. Examples are

• amphibious (able to operate both on water and on land)
• amphiphilic (of molecule etc. having both hydrophibic and hydrophilic components)
• amphimixis (fusion of male and female gametes)

and

• ambidextrous (able to use both hands equally)
• ambilateral (relating to both sides)
• ambivalent (one person having opposing attitudes towards something)

As a pedantic traditionalist, I am not an advocate of inventing words, but it struck me that ambisocial had a plausible ring to it. So plausible, it turns out, that it appears in something that goes under the name of Urban Dictionary. The choice is yours.