Single Activation Falling Edge Detector
If using a flop, please check the power-on state of its output is well determined, which might need a special reset circuit.

Myself, I'd use this:


PNP+NPN wired as thyristor
PNP base acts as trigger
Trigger is capacitive-coupled to your toggling GPIO.


Power-up behavior is known: a thyristor wakes up open.

Slow voltage changes (ie, stuff that happens at supply ramp-up) does not pass through the capacitor, which should be small enough to only trigger the circuit on a fast edge from the GPIO pin.

Just my 2c.