I followed the steps to make the usb boot img on SanDisk UltraFit USB 3.0 Flash Drive. https://www.openos.org/threads/dsm-6-1-3-15152-2017715.29/ However, it does not work on my Asrock J-4205. I tried both UEFI ver v1.2 and v1.3, same problem. I try the usb on other computer, it works. The usb boot device can be detected and start booting. Anyone can help? Million thanks.
Solved, by plugging the 3.0 usb flash into the 2.0 usb slot. (there are 2x3.0 slot and 2x2.0 slot at the back, and 2x3.0 slot at the front). So tricky. All good now. Thanks.