Not that hard to packet sniff or add a firewall

Zoom sends encrypted traffic to their servers, for "control" purposes. How are you sure it's not leaking your company secrets.

There's no way that a legal team will be happy with an attempted technical block to what is a legal problem.

Simply cancel the zoom contract. It's not like there aren't alternatives.

If this applies to corporate accounts then it's time to short Zoom like there's no tomorrow.