Adding an (tiny) example with a struct could also be worth considering.

@eiriktsarpalis Can you weigh in?

We have a supported collection types article already but not a general "supported types". Perhaps it makes sense to generalize it and include explicit mention of all supported kinds, roughly:

Serializing as JSON objects

The following types serialize as JSON objects unless they implement IEnumerable<T>

• Classes
• Structs
• Interfaces
• Records and struct records

Serializing as JSON arrays

(insert existing content about collection types)

Unupported types

• System.Type and System.Reflection.MemberInfo
• ReadOnlySpan<T> , Span<T> and ref structs in general
• Delegate types
• IntPtr and UIntPtr.