I have tried the latest stable and alpha versions.
I assume this has been an issue for a while.
Description:
When mapping Normal Mouse (and other input mapping categories like Trackpad), in the Action "Custom Mouse Buttons & Modifiers(...)" the Click Type "Button: 3" is not available, while the other Button numbers are, and even though Button 3 on a mouse works as a trigger.
Extra information:
I was doing something silly, I wanted to map Mouse Button 3 to Button 3, and Mouse Button 4 to Button 4. But Button 3 is not an available Action, I assume this is an oversight or mistake. When considering if this is a "Feature Request" or "Bug Report" I thought that it leaned more heavily towards the latter.
So the reason there is a distinct Trigger for the scroll wheel click (middle mouse button) and for Button 3 is because certain mice make that distinction? A lot of mice have two buttons on the side. Typically, they trigger Forward and Back (like in web browsers or anywhere else). To my memory, normally those are Button 4 and 5?
This is what I get if I "record a mouse button" using the two side buttons and mouse wheel click:
I got the same results with a few different Logitech mice using their two side buttons and middle-click/(scroll wheel click).
MX Master 2S
MX Master 3
MX Ergo
On a Logitech G602 which has 6 side buttons, the G4 and G5 button "records" as Button 3 and Button 4, respectively. (There is no labelled G3 button, I assume that is Button 3 and thus the middle-click.)