Check the SSD partition boot flag?
Check the bios boot sequence?
Check the SSD partition boot flag?
Check the bios boot sequence?
The second is good. SD, if present, otherwise USB.
How do I check/change the boot flag?
I assume Raspberry Pi Imager should set that, no?
Yeah, not necessarily, because I guess 99.9% folks just want a portable storage device, but don't want to boot from it.