One option are keyed-verification anonymous credentials like used in WabiSabi. There's one implementation by nostr:nprofile1qqsfuv8fgq3cek0ta0rr9qtkm4x3pxqjz22y9u4xcwrj0lrxlfl2jzspz4mhxue69uhhyetvv9ujuerpd46hxtnfduhszrnhwden5te0dehhxtnvdakz7qgswaehxw309ahx7um5wghx6mmd9uv87spp: https://github.com/lontivero/cashabi