To turn fn key lock off repeat the process you followed to turn it on.
Magic keyboard windows function keys.
Select or deselect use all f1 f2 etc.
Click on the apple icon in the top left corner of your screen and then click on system preferences.
F1 opens help in an app or f12 opens the web console in your browser.
If a user account control dialog appears click yes.
If your fn keys by default controlled media e g volume playback etc turning on the fn key lock will make it so that the fn keys now execute the secondary function that f1 f12 do e g.
In order to type the additional third character symbol on some keys follow these steps.
The right command option keys act like the alt gr key on windows keyboards.
Keys as standard function keys.
Within system preferences click on keyboard.
In windows on your mac click in the right side of the taskbar click the boot camp icon then choose boot camp control panel.
Install and activate the belonging magic keyboard layout for your language.
Is the menu or applications key on windows that allows you to launch.
On the following screen ensure that you do not have a check mark in the box that says use f1 f2 etc.
The various models such as the magic keyboard.
Quick video on how to use an apple keyboard on windows 10 and still use the apple volume function keys.