What is the source of the FM on the Moog One's filter section and can I change it?

By default, both filters use Oscillator 2 as the modulation source for their FM amount. However, you can change this to either of the other two oscillators by selecting the MORE window in the filter section and changing the FM SOURCE for each filter.

Note: this should not be confused with the FREQUENCY MODULATION setting in the oscillator section, which allows you to apply FM to the oscillators in three different configurations.