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At least in 2019, it was possible. The GUI connects to the daemon through a TCP socket, and all info passed through that connection (no direct file access from the GUI). It was possible to set it up with the daemon on one machine, and the GUI on another -- though I vaguely remember having to set up an SSH tunnel so that the connection would come from 127.0.0.1 on the daemon machine (not sure it was needed, but I think that's how I set it up).

Not sure about opensnitch, but packet inspection on your local network is what Wireshark is all about.

https://www.wireshark.org/

Pihole, adguard are probably useful.