flyback compensation design
In your comment, you state that the flyback circuit I built in the templates described here is operated in closed-loop while you want the compensator response. It is true, the loop is closed in dc to let the converter regulate at the right dc value. However, because the ac source is inserted in series with the upper side of the resistive divider, it has the effect of perturbing the loop and because of its constant value, it effectively opens the loop in ac. So the Bode plot you draw while observing the voltage across the injection source is actually an open-loop gain response. This technique has been introduced by Dr. Middlebrook in the 70s and is described here. I have explained it in my book on transfer function with several SPICE examples. The SIMPLIS example looks like this:

By probing various points, you can extract:

the compensator transfer function. Here, this is a type 2 with an opto-coupler
the control-to-output transfer function. This is the power stage ac characteristic you need to think about a possible compensation strategy
the loop gain: you can finally check if the compensation strategy is adequate to meet crossover and phase margin goals. The final results are shown below:


Using this technique, you can run the switching converter in dc closed-loop operation while you open the loop in ac for the analysis you need. Using a frequency response analyzer (FRA) in the lab would not be different.