It’s not real.
This is a joke referencing similar tweets he’s made in the past, such as this one:
Hi! I’m a developer for the Mlem iOS client. Join us on !mlemapp@lemmy.ml!
It’s not real.
This is a joke referencing similar tweets he’s made in the past, such as this one:
In Voyager, you need to enable the feature under Settings -> User Tags.
Voyager implements it entirely on the client; it’s not a feature of Lemmy. Therefore it isn’t available via the Lemmy website.
However, PieFed does have backend support for user tagging. On a PieFed account, you can tag users through the website or through Mlem.