Does Bethesda Softworks hold copyright over the world Vault as in if I were to use it in a Fallout themed Youtube channel would it be copyright infringing

Individual words cannot be protected by copyright, and Bethesda has not registered it as a trademark. Keep in mind that Bethesda has registered many words, phrases, and logos related to Fallout as trademarks, so your intended use may be infringing in other ways.