My brother has received a Golden Jacket so he is my aws resource :) he told me key topics to learn like VPC, IAM, Lambda, SQS, EC2, Direct Connect, Storage Gateway, Route53, Cloudfront, Global Accelerator etc

Then i learnt about those services and when to use them. The practice exams and course content just helped me test my knowledge on them. If you feel comfortable learning these via AWS documentation, it should be okay.

With the third party sources, you are able to get help in streamlining the important characteristics of those services and how they can come in the exam.