Read the Microsoft documentation.

Good News:

• The System.Text.Json namespace contains all the entry points and the main types.
• The System.Text.Json.Serialization namespace contains attributes and APIs for advanced scenarios and customization specific to serialization and deserialization.
• The System.Net.Http.Json namespace contains extension methods for serializing and deserializing JSON payloads from the network.

Bad News:

• System.Text.Json doesn't support the following serialization APIs that you might have used previously:

• Attributes from the System.Runtime.Serialization namespace.

• The System.SerializableAttribute attribute and the ISerializable interface. These types are used only for Binary and XML serialization.

Source: Microsoft Documentation