Subdivision behaviour is different than in any other software causing compatibility issues - #15 by postrowski5 - User Feedback - Blender Developer Talk
Subdivision Surface Modifier — Blender Manual
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Pablo Dobarro on Twitter: "Multires Subdivide Simple and Linear modes for sculpting hard surface objects are now in Blender 2.90. Today I also coded the Delete Lower Subdivisions operator. After merging that,
FlightGear forum • View topic - Opposite of subdivide in Blender?
modeling - Is there an unsubdivide function in Blender? - Blender Stack Exchange
modeling - the opposite of subdivide - Blender Stack Exchange