How do you enable MMB on macOS Ventura 13.4

Some mice have three buttons and particularly those used with Unix workstations and X11, but Magic Trackpad does not.

Magic trackpad can emulate a two-button mouse, but not a third button.

Magic Trackpad uses gestures:

… Use Multi-Touch gestures on your Mac - Apple Support

If this is an X11 question, then XQuartz can emulate a third-button paste:

... https://superuser.com/questions/517878/why-cant-i-paste-into-xterm-xquartz#558944

I'm not sure what you're referring to when you say "middle mouse button".

There's no "middle mouse button".

Below is what you'll see when you go to Trackpad settings in System Settings: