The metal insert(s) in your desktop or shelf top may be too deeply recessed.
If an insert isn't flush with the surface, the screw won’t engage and will instead appear to ‘spin’ around without attaching.
To fix this, take a hex key (6mm for Bamboo and 7mm for Laminate) and “back out” the metal insert using a counter-clockwise motion until it’s flush with the surface.
Repeat with other inserts as necessary. Once they are all level, you should be able to attach the top without issue.