Ownership of identifiers, that includes usernames, is regulated by Trademark laws.
If you keep using a moniker, like a username, to conduct trade under it, and/or have it registered as a trademark (which requires you to use it in trade or lose it), then you can legally claim it.
Otherwise, Twitter or any other platform, can do whatever they want with it.
That’s an interesting avenue I hadn’t considered. However, the lack of a registered trademark does not mean the lack of any rights whatsoever.
Correct. What decides the rights, is the use. A registered but unused mark loses the rights, while a used but unregistered one keeps the rights (just becomes harder to prove).
And it needs to be used for trade. Like, someone’s personal nick, not used for trade, would have no rights. But the nick of someone using it to be an influencer, or a furry artist, would give them some rights.
