I’m going to use a PCB Jumper right angle to connect with the FZ device but I was curious as to what you’d think best in the connection wires between the PCBs and the CoB.
I prefer stranded for most connections because it bends easy without breakage. It can be harder to get into a PCB but if you tin the end first that’s not so bad. Solid core can be bent to a shape and stay in that shape. It can be threaded into a PCB hole easily. Solid core is needed for “wire wrapping” which isn’t common anymore but it’s a good old trick I recently learned.
Here are some other opinions.