I hate these Siri suggested replies in the Messages app in macOS 15+ (Sequioa). This post has a fix that actually works.

To disable these annoying auto-replies, go to System Settings > Keyboard > Input Sources > Text Input and disable “Suggested Replies”

The suggestions are mediocre at best, but more annoyingly, they steal keyboard focus and I have to press “esc” a couple times to actually start typing.

There’s a bunch of Apple support threads and this reddit thread but instructions were incorrect, so here we are! Good luck