Hi. I had the same problem after installing Linux Mint on a partition on my hard drive, other partition being Windows 10. After much trial and error and frustration, I finally solved it by setting, under Security in the Bios, a Supervisor Password so I could access the option to Select an UEFI file as trusted for executing, where I entered my Ubuntu boot file and then my Windows boot file (it appears to take the most recently entered as the first priority). The Windows boot file was that one in the boot directory (not in the Windows directory). I also activated the F12 key on the Main menu in the Bios, so I can choose to use Linux when I want, by (repeatedly) pressing F12 when I start up. And I've found that the Boot priority order appears to be ignored - maybe. I set USB as number 1 while I was having issues, followed by HDD, but the USB boot stick didn't work - went straight to Windows instead. Anyway, it's working as I want it now. Good luck.