i think accumulators combined with web of trust might be the magic you are looking for

if you know a few people in common and there is a good chance they are linked one or two steps from this other person it acts as a big set of extra set members to get a result that approaches true/false

what that would probably mean in practise is you would fill in several numbers in one search and when the keys of several hit then it narrows down the identities to a small set, and uses web of trust traversal following the memberships

i'm sure you are gonna bake your noodle trying to figure out a credibly secure method to do this on an async data system like nostr but i just want to keep encouraging you to look into it

i'm sure i'm not the only person with a passing curiosity about such things... cryptography applications are nowhere near a complete set of principles as you see in many other sciences, there is a heap of new combinations of tools that haven't happened yet, combinatorial possibilities in cryptography, so, LFG!