I did try all four combinations and the only one that works for me is the Carto supplied Katapult with Carto supplied Klipper. I was not able to get the other three to enter bootloader via CAN. I wonder if perhaps @Esoterical managed to make it work reliably?
Thank you.
UPDATE:
I can confirm that https://github.com/Klipper3d/klipper/pull/7251 fixes the issue.