I know that an increase in velocity (TAS) reduces the AOA and that makes sense. But how just simply increasing the blade rotation (RPM) results in higher AOA?
Vector diagrams help with visualizing prop blades. Above the vertical vector lines are two RPMs, the horizontal vector lines are the forward velocity (the same for both), and the connecting orange vector lines are the resultant airflows. Note the AOA for the same blade pitch and how it is affected by the airflow at the two RPMs.
Note: that's also why slow/windmilling RPMs result in high drag (negative AOA; airflow hitting top side), and why dead engines are feathered if that's an option.