Check if fast startup is disabled, in many cases (if not all) it needs to be disabled.
Fast Startup - Turn On or Off in Windows 10 - Windows 10 Forums
Then you may also need to change a setting in the BIOS in 'BIOS Features' > 'Windows 8', I'm not sure which one but if it is necessary and disabling fast startup isn't enough then the boot mode needs to be changed to legacy.
I tried those and even tried just completely resetting the CMOS with only the flash drive plugged in.
Here is all of the settings, Tre boot order is wrong. I use boot override to boot from USB usually. Imgur: The most awesome images on the Internet
I tired another USB and still got:
"Missing operating system.
BOOTMGR is missing
Press Ctrl+Alt+Del to Restart
_"
The boot order shouldn't matter, using boot override should only boot from the device I select. But as I said earlier I disconnected every drive except for usb to test it.
I don't think the installer is working properly, is there a better alternative to make bootable usb media?
The boot order indeed doesn't matter in the BIOS (unless a user has edited the boot order what sometimes happens) it was just a question out of curiosity to see if a problem was present in there :)
Boot override shouldn't be necessary, the maximum that one would have to do is choosing the USB device from the boot options.
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