Pathetic! A post on Facebook, but you can only claim your Instagram username! Meta has so many messengers, which don't even interop! I can't message somebody on Instagram or Facebook from WhatsApp!
It's not tied to your app version, today morning I didn't have this option, today evening I have it with same version without update.
Seems you can switch usernames as many times you want, tried at least 5 checking something interesting, though all English international ones seem taken.