Is this differential RC filter needed on a reference voltage?
See JRE's comment below, 100Ω resistor (R100) is used for stability and filtering.
This doesn't really answer the question, but I don't know if this design you are looking at is good for an ADC reference. ADC ref inputs are susceptible to large, high bandwidth current spikes. Having a 100Ω resistance on the output of buffer is a strange design decision. Buffers are used because they have a low output impedance and can help source transient current spikes. The 100Ω resistor will drastically affect output voltage if reference current spikes. The µC you are using has SAR ADCs which can require transient currents. The image below shows a typical ADC reference driver.

This design seems like it's more for a reference that is built for a low noise, no current kind of reference (input to an op-amp for example).
Where did you get your schematic from?

Image source:
https://www.ti.com/lit/ug/tiduck3a/tiduck3a.pdf?ts=1593065295985&amp;ref_url=https%253A%252F%252Fwww.google.com%252F