Reducing EMI emission from 20KHz PWM
20kHz is slow.

Use gate resistors to adjust the MOSFET switching time to keep switching losses reasonable, but not faster.

With 20kHz (ie, 50µs period) you can switch in 500ns. No need to switch in 10ns, that will only generate an enormous amount of EMI.

If you only switch one side of the H-bridge your cable will radiate common mode noise. This can be mitigated by switching both sides in opposing polarities all the time and/or applying a ferrite core on your cable.