Problem configuring extruder on Fly-SB2040 Pro

[bertenvdb]

Klippain branch

• I confirm using the main branch

Version

v4.3.1-18-ga30308e5

Describe the bug and expected behavior

Spider v3 + Fly-SB2040 Pro Max

I haven't looked at my Voron for several months but now have some spare time to continue working at it. Sometime last summer I installed the Fly-SB2040 Pro, and everything worked perfectly (without Klippain). However, I discovered Klippain and I thought it's clean modular config was worth installing, so I did.
I've followed the relevant documentation, but can't get my extruder to work. Everything else on my toolhead works, except for the extruder. Whatever I do, there's always some error. I've been going at this for about 8 evenings now, and desperately need help.

With the config as I think it should be, I get: Unable to read tmc uart 'extruder' register IFCNT

Please help.

Additional information and klippy.log

klippy.log
printer.txt
overrides.txt
mcu.txt

[bertenvdb]

I've noticed config/hardware/mcu_definitions/toolhead/Mellow_SB2040_Pro.cfg contains this definition:
MCU_EMOT_CS=gpio8

But according to the pinout this should be gpio11.

Changing this does not result in solving the problem, Klipper still says Unable to read tmc uart 'extruder' register IFCNT.