On the singular set of the free boundary for a Monge-Ampère obstacle problem

This is a continuation of our earlier work \cite{jin2025regularity} on the Monge-Amp\`ere obstacle problem $$\det D^2 v = v^q \chi_{\{v>0\}}, \quad v \geq 0 \text{ convex} %\quad ,$$ with $q \in [0,n)$, where we studied the regularity of the strictly convex part of the free boundary. In this work, we examine the non-strictly convex part of the free boundary and establish optimal dimension bounds for its flat portion. Additionally, we investigate the strong maximum principle and a stability property for this Monge-Amp\`ere obstacle problem.