Taken from #63686 (comment):

The internal converters for collection and dictionary types do provide similar functionality, and we might consider exposing dedicated constructor delegates for each kind:

• A Func<IList, object>>? CreateEnumerable delegate for JsonTypeInfoKind.Enumerable
• A Func<IDictionary, object>>? CreateDictionary delegate for JsonTypeInfoKind.Dictionary.
• A Func<object[], object>? CreateObjectWithParameters delegate for invoking parameterized constructors in JsonTypeInfoKind.Object.

Note that these would require exposing the JsonTypeInfo.ElementType and JsonTypeInfo.KeyType properties, respectively. The parameterized constructor delegate would require exposing the internal [JsonParameterInfo]
#78098 metadata type.

Related bugs that should be addressed in conjunction with this story:

• System.Text.Json contract customization ignoring custom CreateObject delegates in certain collection types #73382
• System.Text.Json does not support constructors with byref parameters. #46088
• Expose information about JsonPropertyInfo being readable/writable #77307
• S.T.J.JsonSerializer doesn't support properties marked with JsonRequiredAttribute that're initialized through ctor #78098
• [JsonSerializer] Relax restrictions on ctor param type to immutable property type matching where reasonable #44428
• JsonSerializer.Serialize an anonymous type, with duplicate nested names throws an unexpected exception #81550