When I try to use Baritone LegitMine on 1.17.1 (using meteor client) it tells me
"Successfully set LegitMine to false"
"Old value: false"
and nothing happens.

Does LegitMine not work in 1.17?

Please ask this on #2850 as 1.17.1 isn't a supported version of baritone yet.

I'm not sure but I think that your client uses Baritone API and probably it just overrides Baritone settings.