Faced such problem. Bought HP Pavilion 15-ec1063ur with FreeOS. Try to install W10 from USB flash, but it is not in boot list, because the Legacy mode should be enabled for it became visible. But notebook's BIOS have no such option. I can just disable the security mode.
I've not actually done this, since I don't have access to a FreeDOS machine, but I've read that the following will work.
1) Win10 install media format Since the FreeDOS PC will not allow you to select Legacy boot, you must have GPT/UEFI installation media. The typical MBR/BIOS media will not work. IF you created your media from the Microsoft Creation Tool (MCT) and you did not select UEFI, then you can use the free RUFUS too with the ISO file to create UEFI boot media. You can get RUFUS from here: https://rufus.ie/en_US/
If you did not download the ISO file, you will need to do it again to create UEFI boot media.
2) Insert the USB stick into the PC
3) Reboot the PC, pressing F9 repeatedly all the time. You should see the Boot Devices menu appear.
4) Select the USB hard drive under EFI devices
The installation should now start.
***If my post helped, click the thumbs-up symbol to say thanks***
***Please mark Accept As Solution if my post solved your problem***
I am a volunteer and I do not work for, nor represent, HP
Be alert for scammers posting fake support phone numbers and/or email addresses on the community. If you think you have received a fake HP Support message, please report it to us by clicking on "Flag Post".