Drain to Source Current Waveform on Mosfet is Slow
@Andyaka detail Added. I use resistive load only for the load


I beg to differ, clearly there is a 200 uH inductor in series with the output as would be the case in many designs (but different values).

This is the item that causes the slow rise and fall times of current through the drain of the MOSFET. This is the sort of waveform you should see: -



And, if your switching frequency is lowered you will see start to compress at the peaks (as is seen in your picture).

V = L di/dt or, rearranged, if you put a constant voltage across an inductor of value L you get a constant value of di/dt (rising or falling).