Network Subsystem is unusable Error - Proxy Server BTGuard SOCKS5

[jjemil749]

macOS Big Sur 11.6 transmission-daemon 3.0 compiled with homebrew Transmission Remote GUI v5.18.0

Whenever I try to enable the proxy server under Settings > Proxy > proxy.btguard.com (BTGuard) port 1025,

connection fails each time with "Network subsystem is unusable"

I tried changing the port to 80, but I still get the connection error.

The same BTGuard credentials work fine without any problems on Deluge Torrent Client

Transmission Remote GUI doesn't seem to have the capability to produce logs, so I don't know where to start looking for answers.

I do have the short log produced by transmission-daemon, but there's no clue about the connection failure.

transmission.log

By the way, the connection to the transmission-daemon fails also with a strange SSL error pop-up if "Use SSL" is checked under Settings > Transmission. Could indicate some type of SSL authentication issue going on.

ADDENDUM: on Windows 10, with transmission-daemon 2.77 and Transmission Remote GUI v5.18.0, I get the same “ Network subsystem is unusable” when trying to enable BTGuard proxy server, and the same SSL error when enabling “Use SSL”.