i have manjaro gnome edition flashed to a USB drive, and I have just assembled it. when it prompts what to do I cannot use the arrow keys, nor does selection of USB boot work. instead if USB boot is chosen the screen flashes and returns to the boot screen.
the only screen I can get is this
So the arrows don’t do anything because you only have one option to select.
Do you have Secure Boot disabled?
I had the same issue. I’m pretty sure @Rodrigo_Luzuriaga has the solution.
I was under the impression you could only get into the first boot menu and not the BIOS/UEFI on first boot, that was probably wrong. In retrospect, on boot, as soon as you see the Framework logo and you hit F2 you should always get into the BIOS. If you leave it and it tries to boot but finds no OS it goes to the first boot screen.