You should never run a telnet server
The usual warning applies. Telnet is horribly insecure. Do not run a telnet server on your computer. Seriously, there is no good reason to do so.
Instead you can use SSH. If you were specifically interested in inetd-style socket activation, you can still do that with SSH. See
How to run a telnet server
To be clear. You can run
systemctl start xinetd. Running
/etc/init.d/xinet start would probably do exactly the same anyway. However, that is due to special backwards compatibility code in Debian. So I agree it is good to train yourself to use the
systemd tools directly, when your system is using
Anyway, it sounds like you are interested in writing a custom telnet.socket (and telnet.service, I guess) which would match the behaviour you've read people talking about for systems based on RedHat, Arch Linux etc.
The source code for the Fedora package is currently available at https://src.fedoraproject.org/rpms/telnet/tree/master
Create the following files in
Description=Telnet Server Activation Socket