Attempting to compile the following

[InterfaceType(ComInterfaceType.InterfaceIsIUnknown)]
[Guid("7DAC8207-D3AE-4C75-9B67-92801A497D44")]
[GeneratedComInterface]
public partial interface IFoo
{
    [Obsolete]
    void Foo();
}

Generates a warning warning CS0612: 'IFoo.Foo()' is obsolete

Other source generators in the runtime explicitly disable CS0612 and CS0618 obsolete warnings in their generated output. I would imagine the same should be done in the files emitted by the COM source generator