Hello,
Thank you for reaching out!
Please try pinging the remote Telnet server and see if it's reachable. Also, verify that the Telnet port (the default is 23) is not used by some other rule.
This can be done by navigating to Network → Firewall → Traffic rules.
Also, could you provide the command/app you're using to connect to the telnet server? What error are you receiving?
Best regards,
DaumantasG