Thanks for the link, just tried Green Tunnel on the use case where my ISP is blocking me and just managed to change the error from PT_CONNECT_RESET_ERROR to PR_END_OF_FILE_ERROR.

Side note, looks like that if installed by snap on Ubuntu 20.10 it cannot automagically change the proxy configuration in Gnome

  green-tunnel:system-proxy [SYSTEM PROXY] error on SetProxy   (Error: Command failed: gsettings set org.gnome.system.proxy mode manual
  green-tunnel:system-proxy /bin/sh: 1: gsettings: not found

Enabling proxy manually makes it work but yet, it doesn't circumvent my ISP filtering :(