No need gor a china-style great firewall. Just compel your local dns providers to stop resolving that website. That's what they do for copyright violations

Easy to circumvent ? Sure, but most people don't know how, so you've made the website inaccessible to the vast majority

The infrastructure is already in place for a global great firewall. One need only to compel Google and Cloudflare to block a site in their DNS and most of the planet will not be able to reach it.