The number of complaints on NHTSA, independent owner reports, and feedback from Mazda techs, all points to much lower number of cracked NA heads on 2020 and newer models. And if a manufacturing issue with the casting process was the one and only cause for the heads cracking, it makes sense that fixing it would resolve the issue.
All of that said, it does continue to nag at me why there have been ANY cracked heads at all on the newer MYs. The Mazda techs say there have been 'a few' newer ones, and we have had one confirmed report (with dealership paperwork) of a cracked head on a 2022 reported here. So this means that, unless they continued to install previously cast defective heads, the casting issue has not been 100% resolved. Or alternatively, there's more to the cracked head issue than just bad casting alone. Regardless of what the actual answer is, it's disappointing and unsettling to me that this mess still has not been completely resolved, six years or so after it began.
So the answer to your question is that 2020 and later NA/CD models currently appear to be much less likely to have cracked heads. However, probably no one outside of Hiroshima actually knows what the future holds for these newer vehicles.