There's a know issue about compiling the R23 sdk with Visual Studio 16.9.
Trying to compile with this version will lead you to the following error:

Error C2079 'maxon::ResultBase<RESULT_TYPE>::_value' uses undefined class 'maxon::BlendAnimationRef' math.framework <path to the file> 571

This issue will be fixed in the next update.
To fix the issue, open the file objectbase.h of core.framework and change those lines :

around line 1088:

// template <typename I, typename = I*> struct VirtualCreate
// become 
template <typename I, typename = I*(*)()> struct VirtualCreate

around line 1102:

// template <typename I> struct VirtualCreate<I, decltype(I::Create())>
// become 
template <typename I> struct VirtualCreate<I, decltype(&I::Create)>

Cheers,
Manuel