If you are interested in getting an overview of the topics covered on this exam and want to get a flavor for the types of questions asked, review this video I recorded earlier this year for the Microsoft 365 Virtual Marathon.
If you want more in-depth training, you can watch our five day exam prep course for MS-600: Building Applications and Solutions with Microsoft 365 Core Services. Each day’s video maps to one of the objectives for the course. (The duration of the session is listed following the link.) These videos were recorded in advance and delivered on behalf of Microsoft to its world-wide developer audience.