This NIP is not yet in main. Here is an overview of PRs referencing this NIP. 
NIP-41: simple account migration OPEN @pablof7z
 NIP-41: Key Invalidation; using HD (BIP32) derivation OPEN @optout21
NIP-41: Key Invalidation. first draft. CLOSED @fiatjaf
NIP-41: Poll & Vote Event OPEN @0xtlt
Partial-Content - Transmitting file chunks over nostr CLOSED @Egge7
feat: add surveys / polls OPEN @fernandolguevara
NIP-41: Authentication CLOSED @Semisol