M20T Pilot flying reported landing gear collapse on landing rollout.

Narrative

I was the pilot of Mooney; M20T; on an IFR flight from ZZZ1 to ZZZ; the homebound leg for a business meeting in ZZZ1. My clearance was ZZZ2 ZZZ3 ZZZ4 ZZZZZ ZZZ. Weather for the whole trip was solid VMC. I departed ZZZ1 at XA00 and by around XB00 I was being vectored for an ILS XX approach at ZZZ. A mile or two outside of ZZZZZ1 the TRACON turned me over to Tower. Shortly afterwards Tower cleared me to land on Runway XX. As I recollect; at the FAF (ZZZZZ1) I reached for the gear switch (located at the top of the instrument panel) and activated it to lower the landing gear. I heard the customary motor noise and felt the usual drag of the gear. Shortly afterwards; as my airspeed was down to flap speed; I lowered full flaps (the control is located below the bottom of the instrument panel). I felt the effect of lowered flaps. With reduced power I crossed the fence at 75 kts. Indicated and approached the runway until I was about 5 ft. above the surface. At that point I reduced power altogether; pulled up flaps; and felt the flare. I then expected touchdown. Touchdown arrived with an unexpectedly solid bump; although not of a size I haven't experienced in this airplane before. The bump; however; was followed by a discernable drop and a very brief descent leading to the fuselage touching the runway and scraping the surface. This surprised me because I interpreted this to the landing gear collapsing under the airplane. I then observed the prop striking the runway and stopping rotation. After a short slide the airplane came to rest at the western edge of the runway. The slide was gentle and there were no sparks or any indication of electrical problems. I called the Tower and advised. I then shut off the master; turned off all the switches; opened the door; and got out. The airplane was resting on its belly in level attitude. I clearly remember reaching for the gear switch and pulling and moving it toward the gear down position. I also remember hearing the sound of the motor and feeling the draft of the gear. I also clearly remember dropping flaps; and shortly afterwards; doing my pre-landing final check [I] touched the gear switch and announcing 'gear down'; looked over my left shoulder to visually verify full flaps down and announcing; 'flaps down'; and [announced] that all I had to do now is 'manage energy'. To me the landing felt like the gear collapsing after the bounce. After inspecting the main gear; it appeared to me that the gear was not fully retracted into its usual position; completely inside the wing. It was in a position slightly below the wheel-well by maybe 6 inches (the tire was visible and it should not have been).