I'm a bit of a n00b when it comes to using BTT, though I've created a few minor actions with BTT. I'm now wanting to use my new Logitech MX Master 3S with BTT, but I'm not sure which device to choose in BTT, as it's not a Magic Mouse, Trackpad, or Normal Mouse (that I'm aware of). I tried using "Normal Mouse" and using the middle button as the trigger, but it didn't work. Is there another device that I should be using? Or ... ?
I think @Andreas_Hegenberg Will be releasing support for MX master. Maybe.
Waiting for that too 
Waiting for my MX Master 3S delivery. Is it worth the hype?
For now, you can go into Logitech's software, set-up keyboard shortcuts for the buttons, then setup those shortcuts in BTT [Keyboard Section] and assign the actions you want.
Update: Tried doing a Scroll up + Shift Modifier key to increase the volume
The scroll-up is detected in BTT settings, but it doesn't work in practice ( in Normal mouse BTT Menu)
Normally it should work since BTT Detected it, but for some reason, it doesn't 