Windows 10: How to change boot options permanently (Win 10 not being default)?

Unfortunately not. Only Windows 10 is listed.

 

It looks that way. I can positively confirm that hibernation and fast startup are disabled. The boot behavior and the "cannot mount" message in Linux suggest that Windows is in a hibernated state anyway.

 

Did you set the Timeout to 30 (seconds ) ?

 

No, cause only Windows 10 was listed in the first step already.

 

The reason I asked you to set it at 30 sec is to give the system a chance to list both OSes so that you would have a chance to choose which one to run.
Humour me. Set it at 30 sec > click OK when done > restart computer......................

 

I didn't pay attention to the Timeout field, I just checked and it was already set to 30 seconds by default. Can't work though if Linux isn't recognized as an option, right? I'm not sure if getting it listed from within Windows is possible because Windows doesn't support the ext4 file system that my Linux installation is on.

 

Will it boot from the external drive if you disconnect the drive Windows is installed on? I think it's something in the bios. You could try a bios update if one is available for your computer. Use caution though. A failed bios update can make your computer useless.

 

I tried a few more things, for example disconnecting the Windows drive as Winuser suggested. Without the Windows drive, Linux came up fine. Then I reconnected the Windows drive, started up, and Linux booted! So I thought the problem was solved, until I shut down Linux and booted again. Now it's the same thing as before - Windows comes up every time. What's going on?