Is there still a way to load Telnet on OS10.13

See if you can send the necessary telnet commands over with the curl tool. Something like this:

curl --telnet-option TTYPE=vt100 telnet://example.com:23

A direct build with the command-line tools without Homebrew probably still works. With the command-line tools installed, and that would look something like this:

xcode-select --install
curl -o https://ftp.gnu.org/gnu/inetutils/inetutils-2.4.tar.gz
tar xzf inetutils-2.4.tar.gz
cd inetutils-2.4
./configure
make
sudo make install

For assistance with Homebrew, check with the Homebrew folks.

On Xcode that far back, I don't recall the particular location of the installation within Xcode. On semi-recent Xcode, use Xcode > Preferences > Location > Command Line Tool > Select the command line tools version

This article suggests skipping the "sudo make install" and copying just the (insecure) telnet and ftp clients into /usr/local/bin. The reason being that "sudo make install" supposedly copies in a whole bunch of commands that "do not work as expected afterwards."

https://www.unixfu.ch/get-telnet-and-ftp-client-back-on-macos-high-sierra/

Servant of Cats wrote:

This article suggests skipping the "sudo make install" and copying just the (insecure) telnet and ftp clients into /usr/local/bin. The reason being that "sudo make install" supposedly copies in a whole bunch of commands that "do not work as expected afterwards."

https://www.unixfu.ch/get-telnet-and-ftp-client-back-on-macos-high-sierra/

Good info. I usually use the Serial app, which does a whole lot more than does the GNU telnet client. And when I’ve needed the old-style telnet, the curl stuff has worked, and homebrew has worked—but I’m also running a rather more recent macOS than macOS 10.13.