I've broken carbon seat posts before too. I find it helps to have an oversized, dual layer seat post clamp like https://a.co/d/aJQYU0P and line both layers with rubber. I think the pros even tend to use very low Nm tightness and just slap a second, undersized seat post clamp above the seat tube to prevent the seat post from slipping down despite the super low torque. Then you also have to baby it during use like making sure a lot of the post sticks down into the frame. Never pop it most of the way up.