So sharing cookies would imply that you have api.domain.com for your backend and you have frontend hosted on different subdomains (a.frontend.com and b.frontend.com) and you want your frontends to share sessions
Multiple api domains would imply that you have one single frontend frontend.com and you have multiple api endpoints api.com and api2.com
If the two NextJS api layers are on different domains then yes you need to use the multiple endpoints guide