For me, when the hardware first boots I have the screen telling me to push ESC for boot menu
Then on boot menu, I have options to press for booting internal drive or flash drive:
I press 2 to boot flash drive, and it looks like this:
My flash drive boot screen looks like this if I boot Librem 14 laptop from the pureos installer flash drive.
But you said yours is different and says Casper and Gnome live. I am less familiar with that. Do we know why yours is different?
[Edit: Added more images for clarity. I am of course assuming that Librem Mini v2 is running the same stuff as Librem 14 hardware, so correct me if I’m wrong.]