It is client specific.
@username works in Damus.
(but perhaps only if the user follow each other)
dtonon / daniele
npub100…8vwqk
2022-12-21 22:19:37
in reply to nevent1q…9rm0
Author Public Key
npub10000003zmk89narqpczy4ff6rnuht2wu05na7kpnh3mak7z2tqzsv8vwqk