> Are you interested in detecting local 'key up' events over an SSH connection without involving an X server? Oh boy, are you in for a disappointment! It turns out, that it's impossible. I don't mean the "I tried really hard and couldn't figure out how to do it, so it must therefore be impossible" kind of impossible, but the real kind of impossible where the keyup event doesn't get communicated at all during a non-X forwarded SSH session. Here is an experiment you can do to prove this to yourself [...]

This isn't really a good experiment as it assumes that everything that can be sent over SSH will always be sent. This not the case in the terminal world where by default you get a processed character stream and have to explicitly enable anything else. For example kitty's keyboard protocol [0] mentioned elsewhere in this thread needs to be activated by sending the escape sequence CSI > 1 u to the terminal on the other side of the SSH connection.

[0] https://sw.kovidgoyal.net/kitty/keyboard-protocol.html