I had the same problem of startup.nsh.
I’ve accessed the BIOS and simply swapped the boot order instead of disabling, as shown in this guide:
https://youtu.be/3c1EhJbQibE
To access the BIOS, if you have already installed win10, you can follow this guide, made by Samsung but that obviously works on all win10 devices:
https://www.samsung.com/us/support/answer/ANS00048443/#:~:text=Open%20the%20BIOS%20settings%20with%20the%20keyboard&text=Press%20and%20hold%20the%20F2,until%20the%20BIOS%20screen%20displays.
(Click on “open BIOS settings”).
