For the time being I have a Dual Boot machine with Windows 10 and Fedora. I want my machine to ALWAYS boot Windows as default. And when I want it I can select Fedora during boot.

#ALWAYS BOOT PREFERRED OS in Dual Boot (Fedora / CentOS / Redhat

The /boot/grub2/grubenv file cannot be manually edited. Use the following command instead:

# 3 is the line from bootmenu. First line = 0
$ sudo grub2-set-default 3

#Check entry
$ sudo grub2-editenv list

See video for example and more detailed info. Let me know if it helped you.

This is for a standard install where you have not edited bootloader options.