Most password managers will already do this, right? Like the iOS and Firefox built in ones will remember a username/password pair.

they mean generator

Hmm.

There are various fantasy name generators, for D&D and the like.

that is built into bitwarden actually

Yes also with plus addressed E-Mail, or a catch-all E-Mail generator or if you use Firefox Relay etc a generator for these. But the username generator is just a random English word plus a number.

I'd never heard of Firefox Relay, thanks for that.

https://relay.firefox.com/

I find lastpass's generator acceptable. https://www.lastpass.com/features/username-generator

Use a D&D character name generator