Add apps to Input Monitoring
The core question here is "What have you done to make / install any application that would request this entitlement?"

A system call by an app you install and then run is what populates this preference pane. Additionally - there are several entitlements, so you might need to allow an app like Microsoft Teams several clicks for screen sharing, controlling the input, accessing the camera and microphone, etc...

I’ve found as I get used to this release, stating from the top of the pane and looking at each in sequence helps to get used to the different security restrictions.