My Sweet Potato arrived with a dead SD card slot, so I was never able to boot from that. It sounds as if you might have the same issue.
Instead, I boot from USB, and (now) from eMMC. You can set the boot order as detailed here and here (and note that there’s other useful information in those threads).
There’s no need to abandon Libre Computer over this. RPi boards have their own significant disadvantages. You encountered a problem, and there’s probably a workable solution.