And here’s the correction for the OP:
Now, since the block diagram representation of the signal flow has proven to be incorrect, it’s much simpler.
Simply set for your in-ear Out in “CONFIG - OUTPUTS - Input Send Levels” to Pre Fader.
This will make not only all input channel faders in this mix independent of the MainLR, but also your FX Returns.
As Frenchi demonstrates in his images, you can therefore keep an FX closed in the MainLR mix and open it only in the in-ear Out mix.