I 3D printed some, that screw over existing uk switches using the original screws. They have a slot in them so that you can use the switch with a ‘key’ that fits in the switch cover should you ever need to use the switch.
It is a replacement flat light switch. The slot is for a key so you can flip it from on to off/off to on. The key comes in the package. I have a drawer full of these keys I only need to use them if for some reason one of my smart bulbs “hangs” and needs a reboot (very rare). Also comes in useful if you have to replace a bulb and need to get it into pairing mode!