The sites of different delivery services are very different, each with their own odd logic, usually puzzling, always wanting to know your location. Therefore, going to such sites, and even more so, searching through the mail archives for a letter with a tracking number is not a pleasant procedure.

Fortunately, a developer with a name familiar to my ear, Ivan Pavlov, created the application Parcel, which I have been using with pleasure for several years now.
It allows you to track multiple parcels in one simple interface.
It has macOS, iOS, iPad OS applications with synchronization.
It supports many delivery services around the world.
You can see the route of the parcel on the map directly in the app.

Parcel screenshot

Free for tracking up to 3 parcels at once.
For about $3/year, you can remove this restriction and get a few more nice features on top of that.

2020-05-19 Edit