How to determine electrical box size per NEC
You count all wires that depart the box
When dealing with box fill, you have to count all the wires that depart the box (NEC 314.16(B)(1) is phrased &quot;Each conductor that originates outside the box and terminates or is spliced within the box...&quot;), no matter which direction they're running in the circuit topology.  Note, however, that while you need two hots and two neutrals running through the LFMC, you only need one grounding wire shared between both circuits. (Think about the case where the conduit's the grounding path.)
Note also that you only need to count 1/4 of your grounds for box fill. (It used to be that you only counted one ground out of the entire grounding bundle in the box, but that changed in 2020 to deal with boxes that had loads and loads of cables entering them.)