With some friendly hint from another user (thank you Michael):
Be sure in System Inventory the “Knob Mode” of FIT (or Classic Surface) is set to “Pan / Gain / Plugins”.
Then, when opening a GEQ, the Encoders must be set to “Plugin” (Encoder knob right is lid orange) and in the opened GEQ the Faders Button on top is pressed (lid blue), then the faders change to GEQ!
Because I never used the Encoder Edit mode for Plugins, it was deactivated therefore GEQ on faders couldn’t work.
Now we just need to figure out how to reliably switch the fader range (bottom half/top half of the GEQ)
It seemed like tapping a fader would move it, sometimes, and then sometimes moving the faders would randomly shift the range up or down. I couldn’t figure it out.