How do I check the engine (Biturbo V6) oil level on my 2019 E450 4MATIC Coupe?

What is your question?

The instructions in the Owner's Manual and online did not work. Emails to the dealer and a chat session with another have not been answered.

What makes this problem better or worse?

Lack of dealer response.

How long has your 2019 Mercedes-Benz E450 had this problem?

A couple of days.