Ignore what you have read about the new engine making the MAX unstable. It’s more nuanced: It’s unstable near stall.

Commercial aircraft are not fighters. They don’t need to be unstable with computers making them flyable. An unstable airliner would be an uncomfortable airliner and hence a commercial disaster.

What has changed is whether or not there is a manual connection between the yoke and the control surfaces. For reasons of cost, that connection has been going away.