It's probably just DNS (port 53). It's the way Europeans tend to implement their censorship, with the ISPs as executors. It's trivial to bypass, but most non-technical users don't know how, so it's good enough to comply.
They also have a wireguard VPN service called 1.1.1.1 (with WARP). My understanding is you basically VPN into a cloudflare datacenter so you don't have issues with cloudflare IPs being blocked