Strike Box aka Dust Box

Slip this strike box behind the strike plate on your door frame to give it a neat & clean look. This hides any imperfections in the recess and stops dust from migrating out of the wall cavity. It is sometimes called a "dust box" for that second reason.

The Fusion 360 (F3D) file is fully parametric. The STL file is sized for my interior doors but might not fit yours. Go into Modify -> Change Parameters to adjust the sizing.