The documentation located here for the Angle field of the Bevel Modifier's Limit Method function reads (emphasis mine):

Angle
Only edges where the adjacent faces form an angle smaller than the defined threshold will be beveled. Intended to allow you to bevel only the sharp edges of an object without affecting its smooth surfaces.

The hover description of this field in blender 2.90.1 reads:

Angle
Angle above which to bevel edges.

The word "smaller" in the online documentation should probably be changed to a "greater".

Using blender 2.90.1