Alas, the real “telnet” protocol has considerably more fanciness than nc. It’s just that the telnet cli command degrades into a simple line-oriented mode if it doesn’t see the telnetd init sequence.

True, but it handles 99% of the use cases of the people who lament the demise of telnet in macOS. :-)

For the rest: brew install telnet

macports please

Here you go:

    sudo port install inetutils

Better. Thank you :)

I read that in Chris Rock's voice. :-)

For example window size negotiation