I’ve an interesting issue with the display. You can turn the display off by setting the BL pin to low.
However, if you then shutdown your pi, but don’t physically remove the power to the pi, the displays screen with turn itself back on during the shutdown and stays on. Which is somewhat annoying.
I’ve tried multiple BL pins to see if that has any effect. But it doesn’t seem to.
The only one I’ve found so far is by putting a transistor between the power/gnd and use another pin to control that. Although possibly I could use the BL pin for that (haven’t tried).
Currently I’m using PWM on the BL pin to dim the display. It works for me, although the BL pin is somewhat a mystery. If the display is on (whether I’m using pwm or not) and I remove the BL pin, the display stays on.
So it seems to be more of a toggle.