Unfortunately there is no way to block websites at the network level (that I know of) as browsers and mobile phones have started using hardcoded DNS resolvers, so the utility of this is limited.
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Most apps I've tried (and browsers too) can be blocked just fine via DNS. The gli.net interface allows "Override DNS Settings of All Clients" and "DNS Rebinding Attack Protection". This way, the router itself is the only resolver actually reachable. Even if I try some manual `dig google.com @1.1.1.1`, I still get the routers result.
The only thing it can't block is DNS over Https. I think that's by design, it seems it's impossible to block that.