Apple's documentation [1] says

Observation doesn’t require a property wrapper to make a property observable. Instead, the accessibility of the property in relationship to an observer, such as a view, determines whether a property is observable.

If you have properties that are accessible to an observer that you don’t want to track, apply the ObservationIgnored() macro to the property.

[1] https://developer.apple.com/documentation/swiftui/migrating-from-the-observable-object-protocol-to-the-observable-macro