So at these different positions I marked my trail wrist and shaft angle with a yellow line.
is the goal to keep this shaft angle the same throughout the entire golf swing? I wasn’t able to really achieve that.
If we are supposed to keep the angle the same, then what’s the best way to practice this?
Good feels! Keep the "wedge" of cheese throughout the golf swing and as long as the arms are straight, you can hit all of the swing "positions" without thinking about them.
That feeling of "whole new downswing" is good - it tells me that you're making a change. If the swing felt comfortable to you, it would indicate that nothing has changed in your swing.