You are looking for an outbound firewall

Like the others recommended

OpenSnitch has multiple detection ways, eBPF might require activation in the kernel, there are others too, 4 in total

For me on NixOS it worked in eBPF and proc mode. NixOS' weird binary placement makes rules less secure I guess as it can only check commands (if it were nix-native it could use a function for that)

And I had tons of "unknown process"es which I needed to allow to not break things, which kinda makes the thing useless