I have been studying for AWS Certified Solution Architect Associate for many months. I finally took the test this weekend. I wanted to document the preparation materials I used.
I started with AWS Certification web site: https://aws.amazon.com/certification/certification-prep/
I read frequently asked questions page for all AWS services: https://aws.amazon.com/faqs/. I also specifically read all the white papers included in well architected framework: https://aws.amazon.com/architecture/well-architected/
I also read test preparation guide: https://d1.awsstatic.com/training-and-certification/docs-sa-assoc/AWS-Certified-Solutions-Architect-Associate_Exam-Guide.pdf and read over sample questions: https://d1.awsstatic.com/training-and-certification/docs-sa-assoc/AWS-Certified-Solutions-Architect-Associate_Sample-Questions.pdf
Finally I took Udemy course: https://www.udemy.com/course/aws-certified-solutions-architect-associate-practice-exams-k/
I also when through sample questions book: https://www.amazon.com/Practice-Questions-2019-800-Guaranteed-ebook/dp/B07YG6NNW3
I hope this is helpful for some folks.