Ok, I was trying to get it working on and off, for some time now, and i finnaly figured it out, so i'll post it here if anyone in future would like to do the same.
Here is how you toggle mangohud using Right-Shift + F12 shortcut. I couldn't get it to work, and after consulting here, i thought that it was something up with wayland input permissions, but it turns out, that you have to simply split the f12 input from Key(F12, Click), into Key(F12, Press), and Key(F12, Release), and put them respectively on key down and key up.
Finnal setup uses Simulate Input from the OpenDeck Starter Pack, and looks like this. Hope it's helpfull in future :)