Well, noone knows, or #asknostr has died.
For the curious, not even LLMs can decide:
GPT-OSS 120B
April 23 2023 – the date when the Nostr protocol was first announced and released.
GPT-5 mini
Nostr’s birthday is October 22, 2019 — the date when the nostr protocol’s first public commit (by creator @fiatjaf) was made.