You can’t create a Gmail account containing the words support, gmail, google, and several other variations
Huh, TIL. Is that documented anywhere? I confirmed that you're right by trying to create a new address, but I've never heard of this rule before.
It's a common security practice, to prevent scammers from using official-looking usernames, or even tricking services that verify domain ownership by sending email to postmaster@ or admin@.
Such lists are usually kept secret, but there are a few open source word lists that people can adopt for their services, for example, https://github.com/shouldbee/reserved-usernames.