Is there a way to invert the FN keys lock in a Microsoft designer Bluetooth Keyboard?

@Ovidiu's method really works. But in fact you don't have to hold for 10 seconds and neither hold Caps+Fn at the same time! You simply press Fn key once and make the led on the key light. That means Fn is disabled and you can use F1, F2, ... as usual. To enable Fn again, just press the Fn key again to turn the light off. Really easy but not that easy to find! ^_-

Actually, Caps+Fn works. I really don't know how I did it but trust me, it works. Press Caps key 1st and Fn key immediately after. Hold for 10 seconds and press Fn key again. You will see a small led turning on. That means you can now use your F keys without pressing the Fn key.

Just hold down Fn key first, then press Caps Lock once, it will be inverted immediately.

For the Microsoft Designer Compact Keyboard, you can use the Microsoft Mouse and Keyboard Center app to configure the default Fn state, and I assume it also works for the full-size keyboard. Helpful if you've remapped Capslock to Left Control.

Support page

Microsoft Mouse and Keyboard Center app download