Flyback diode: it has one job, but mine sucks at it, why?

Easy peasy said:

Looking at your blue trace it is not too bad, a small snubber should compensate, smaller C (x 0.3 or smaller, and similar or larger R)

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If you go to 5x the junction capacitance (~ 50pF) then a 330pF or 470pF cap should be heaps and you will have to experiment to find the correct R value (100 ohms starting..?) 0805 or 1206 directly across the diode. X7R dielectric as a minimum, preferably C0G (NPO).

A snubber across the driving fet can be of benefit too.

The power in the snubber R will be V^2 C Freq so for 10V, 100kHz, 470pF ~ 47mW, 10MHz = 470mW.

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