FM the problem is not responding to amplitude changes but frequency
changes. So any system that can count and measure frequency and
render a pattern based on changing frequency.

Synthetic PLL or simple a software PLL. would do it.
The synthethetic PLL approach means a software oscillator locked
to a varying frequency external signal. The error word generated is
the demodulated signal (apply to D/A or use raw).
A digital detector will have problems if the SNR is to low! If the SNR is
high enought, the all-digital system is just simpler to realize and consumes
lower power.

You need good dynamic range up to the first selectivity that can
remove offending close in signals.

Then you can limit hard. If you limit before or without adaquate
selectivity you will have intermodulation problems.
Superposition prinzip.