Keyboards have an entire row of keys at the top, above the number keys, that are labelled F1 to F12. These keys are present on practically all keyboards regardless if they’re for Macs or PCs. These keys perform two different functions; as Fn keys they have a separate action and as a secondary action they control the volume, brightness, music playback etc.
On a PC, the default function of the Fn keys is set in the BIOS. Your keybaord has an Fn key that, when held down, will allow you to use the secondary action of the Fn keys. Some laptops let you lock the Fn keys. This is like turning Caps lock on which allows you to type all capital letters. The Fn key lock works the same way. When you turn it on, it’s like you’re holding down the Fn key.
Lock key feature
Not all keyboards have an Fn key lock. This is purely subject to the make of a keyboard and is not something to do with drivers or a Windows 10 feature.
The Fn key lock is enabled by holding down two keys; the Fn key, and the Fn lock key. The Fn lock key is usually the Escape key and it will have a padlock on it (see image below). The lock may be present on some other key so look around. If it isn’t present on any key on your keyboard, you cannot enable Fn key lock.
Turn on Fn key lock
To turn on the Fn key lock, tap and hold the Fn key, and then tap the Escape key (or whichever is the Fn lock key), once. Release the Fn key after and the Fn key lock will be on.
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. F1 opens Help in an app or F12 opens the web console in your browser.
To turn Fn key lock off, repeat the process you followed to turn it on. Tap and hold the Fn key, and tap the Escape key once. Release the Fn key.
There’s no way to force a keyboard to lock the function keys. You can probably put an AutoHotKey script together that will allow you to toggle the Function keys however, if you find you often need to use the secondary action of the keys, it’s better to just change their default behavior from BIOS.