Passed DP-900!
Passed DP-900 2 weeks back with a 981.
The standard advice treats this as a vocabulary test. Memorize services, memorize definitions, sit the exam. That works for a pass but bleeds points on scenarios, and there are more scenarios than people warn you about. Plus, this was my first Data specific certification and I intend to do more in the near future, so it was important, even with a 900 level exam, that I was building a good foundation for the future DP-600 certification exam.
So, what worked: learning the why before the what.
If I were starting again I'd drill the three workload categories (relational, non-relational, analytical) until classification is automatic. Every scenario question is really a workload-classification question wearing a service-selection costume. The rest of the exam gets dramatically easier once that's instant.
Skip deep T-SQL. Skip memorizing every Synapse component.
I took about 5 weeks of evenings to study for the exam and probably overstudied in the process! :)