Spring Cloud Gateway and NGINX
I am using NGINX as reverse proxy, but i thought about the same question and i tried (same thing for me. oauth2 authorization-code flow authentication). So, you can serve static content with just Spring Cloud Gateway, it is possible.
For example if you are using React, take build and copy all build files to under resources/static/frontend-name location. Then, disable (permitAll) web security in that all frontend locations. So you can access just typing http://gatewayserver/frontend-name/index.html
However, I don't think to use it in production environment, NGINX still sounds like better idea for me. Because when I take release for frontends, why do i need to take release for gateway at the same time or vice-versa? But, if you have small project, it might be an option.