I am now back and booting, thank you @digitalrayne for capturing this process so clearly.
I used Dupont cables to connect the J21 headers, and I found it useful to use a right-angled USB-C connector with the SYSUSB socket since there is not a lot of room between it and the case hinge.
I initially had some confusion because I was flipping the 1/ON switch which you did say was the wrong one, but somehow I convinced myself that must have been it. Here’s my additional highly detailed annotated guidance to others!
Thank you thank you. Now I shall try to avoid messing with uboot, and focus on other things!