PieFed has the ability for a moderator to restrict votes for all posts within a community to just members, not on a per-post level. Not sure if this is what OP wants.
Also, it is really more of just rejecting and not federating out votes from non-community members. The votes from people on remote lemmy servers would still be counted just on those servers. Federation across servers and software is weird that way sometimes.
PieFed has the ability for a moderator to restrict votes for all posts within a community to just members, not on a per-post level. Not sure if this is what OP wants.
Also, it is really more of just rejecting and not federating out votes from non-community members. The votes from people on remote lemmy servers would still be counted just on those servers. Federation across servers and software is weird that way sometimes.