Yeah, I'm also just getting blank panels.. Mojave 10.14.6

Same here. Tried different interfaces. Nothing.

Another poster did mention that a similarly named utility already exists on MacOS. Perhaps you’re invoking that instead?

Yes name is not unique and conflicting with existing tool. I'm launching exact this utility by defining path as

  ~/.cargo/bin/what

or

  sudo ~/.cargo/bin/what

Catalina: getting "failed to listen" when running non-root, Shows empty panels when ran with sudo.

You can run as non-root by using setcap to give extra capabilites to the binary:

  sudo setcap cap_net_raw,cap_net_admin=eip <path_to_what_binary>

setcap is Linux-specific thing. Doesn't exist on freebsd, darwin(macosx) or any other unix.

yep, on macOS 10.14.6 the command starts but the panes stays empty (silent error) because of SIP "Sandbox: lsof System Policy: deny(1)"

Is there a way to fix this?