Your sample code using fromMatrix to substitute the supposedly deprecated CFrame eye and target constructor does not provide identical functionality in certain edge cases. This is pointed out by Egomoose in the following post: Is CFrame.new(Vector3 position, Vector3 lookAt) actually deprecated? - #4 by EgoMoose
I discovered this discrepancy the hard way when I discovered that my math would come out completely incorrectly when using your (and the devhub’s) substitute sample code using fromMatrix, and would only return the expected output when using the legacy constructor.
I do not wish to downplay your work here on explaining how to use fromMatrix–the diagrams are great and everything is explained with diligence; however, I do wish to make a statement here (since this post will likely be seen by Roblox engineers at some point) that I do not believe the legacy CFrame.new ( Vector3 pos, Vector3 lookAt ) should be deprecated. It is compact, very easy for beginners to understand and work with, and contains behavior that is not matched 1:1 by the substitute.