Since 5.5 TObjectPtr<> is mandatory for UObject variables (only for members of classes and structs). You still need to mark the variable with UPROPERTY() or the UObject ref will never be cleared.
More info for converting between rare ptrs to TObjectPtr (ObjectPtrDecay, “)
In Target.cs see also NativePointerMemberBehaviorOverride using enum PointerMemberBehavior.