Hi @gerhold-ten-voorde
Yes, you are correct. Pin 56 is the signal "FORCE_USB_BOOT". It is default weakly pulled down by the SoC.
To enter eDL/QDL mode, this switch connects a 2-2.2K pullup to VREG_S4A_1P8 (J3 pin 47).
So, on M0154, the default OPEN/OFF position does noting, when ON it enables the pullup.
Hope that helps.
Thanks!
Vinny