SerializedObject

Getting/Setting Managed References

Getting a managed reference out of a SerializedProperty is very challenging¹⁾. It's better to just use C# reflection on the original object and force the asset / object to re-save.

See:

https://forum.unity.com/threads/setting-a-serializedproperty-to-a-struct.521752/
https://answers.unity.com/questions/1347203/a-smarter-way-to-get-the-type-of-serializedpropert.html ²⁾

Pages that link to SerializedObject:

PPtr
RenderSettings

¹⁾

From version 2021.2 on, managedReferenceValue is not Write Only and can be used to easily get the assigned object.

²⁾

This link has very poor code, but the general approach is correct. It is missing many corner cases, including inheritance and private fields, etc