The minimum DIM frequency is determined by the length of the internal counter used to sample the signal. As the MAX20056B uses a 10MHz clock to sample the DIM signal, less than 100Hz is not supported. Much higher frequencies are supported, however since the minimum guaranteed output pulse width is 500ns the dimming resolution suffers at higher DIM frequencies.
For example:
A dimming frequency of 100kHz would only give a dimming ratio of 10us/500ns or 20:1.