Agreed that would help, but even if everyone were to eat, say, half the amount of meat they would normally eat that would be huge.

No....because it would make no difference.

https://youtu.be/sGG-A80Tl5g?si=dAqbVb9JV_uzLRl1

That video is quite biased. Just tell your clanker to critique it. It will point out that those numbers are quite cherry picked, and leaving out important details. E.g. the „GHG would reduce by only 2.6%“ study assumes that all crop production stays the same, which doesn’t make any sense.