I attempted DP-600 exam today and scored 687 (just.... urrghh!!!). Here are key takeaways that may help others-
Time management is key. Mark the questions you are not sure about and move on!
For first timers, you can refer to MS Learn documentation on your test screen. Leverage that but only after you have answered all the questions you are sure of.
Focus on the concepts you are comfortable with. In my case, I don't have a background in PBI and ended wasting A LOT of time going through MS Learn resource browsing through different topics. If I had spent more time on questions with data engineering concepts such as Data Ingestion, T-SQL and PySpark, I would have scored MUCH better.
From standpoint of topics to cover, for people like me who don't have exposure to Power BI, I would recommend get a good understanding DAX Studio, Tabular, DAX Queries(this for me is a wild wild west but some fundamentals will come handy), measures and calculated columns. I saw a lot of questions from these topics.
Sound understanding of Shortcuts, Direct Query and Direct Lake will help.