Take your time on the Lat Activation to feel the lats, & carry that over into the Strict Pullups.
Pull-up by Pulling Down
The power to do a pull-up comes from properly activating the lats, via the elbows. Sure, the biceps are worked, and contribute, but the lats do the driving. Activate the lats by pulling from your elbows, ‘aiming’ or ‘leading’ with them. To feel your lats contract, stand straight, and with scaps retracted (shoulder blades pulled together), reach your hands down your sides as far as possible.
WHITE-ORANGE should focus on consistent movement through the entire rep/negative. Do only as many reps (seconds) as you can accomplish with high quality. BLUE-PURPLE+ should push the weight, but only as quality remains high.