That's uMatrix (at least in-browser)... Sadly it appears to have been discontinued by gorhill.
IP whitelisting isn't fool-proof though. For example, I run an anti-censorship DoH resolver "IP fronted" by Cloudflare specifically to be a hard target to block at IP layer. I mean, you can block Cloudflare's IPs but that'd mean you'd end up blocking other websites too.
Don't think u/gorhill would be inclined at the idea of handing over the reins after the uBlock.org fiasco. Forks may survive, but the extension looks to be all but dead.
IP whitelisting isn't fool-proof though. For example, I run an anti-censorship DoH resolver "IP fronted" by Cloudflare specifically to be a hard target to block at IP layer. I mean, you can block Cloudflare's IPs but that'd mean you'd end up blocking other websites too.