Is there a fixed syllabus for dMAT preparation, and where can I find official practice material?

No, there is no chapter-wise dMAT syllabus in the traditional sense. The format was developed and standardized by g.a.s.t. in cooperation with the Universities of Ulm and Kassel, and it does not change between test dates, so there is nothing to memorize the way you would for a content exam.

What the dMAT actually tests

The Core Module tests reasoning speed through three fixed task types, and the Subject Module tests applied academic reasoning rather than memorized content. Because the format is stable, familiarity with the task types matters far more than any syllabus.

The only official practice material

The sole confirmed, official practice material is the free Preparatory Materials for the General Academic Module published on the g.a.s.t. and d-mat.de portals. It is the only source with detailed task instructions and worked solutions that reliably matches the real exam format.

Work through every exercise twice: once untimed to learn the underlying logic, and once timed to build speed.

My Advice

Download the official g.a.s.t. preparatory material this week, before anything else. It is the only source guaranteed to match the real exam's format, and starting here first prevents you from wasting early preparation hours on third-party material that may not reflect the actual test.