Leaderboard

There's probably better resources, but I skimmed that one, and it had some interactive graphics that explain what goes on.

looks like you're applying yaw and pitch swapped during partial ticks. That is, you're applying a large yaw change to the pitch angle and a small pitch change to the yaw angle. As for how the matrix works, you'll want to read up on projection matricies: https://jsantell.com/3d-projection/