You can install Telnet on Ubuntu 20.04 or 22.04 by following the instructions provided by Linux Capable in their tutorial.
How to Install Telnet on Ubuntu 22.04 or 20.04
Learn how to install Telnet on Ubuntu 22.04 or 20.04 LTS with easy steps. Secure Telnet with UFW firewall and use examples of Telnet commands.
How to Install Telnet on Ubuntu 22.04 or 20.04 - LinuxCapable