There are many excellence posts about this subject so I will not repeat them instead I list those at the end of this post.
I will give you which courses I took and briefly describe how I use those courses to prepare for my exam.
I started with this free course to get myself an orientation of what to expect for this exam.
https://www.aws.training/Details/eLearning?id=34146
Master your DevOps knowledge by training by becoming a certified AWS DevOps Engineer - Professional with our course.
I bought the e-course from acloud guru and this course only gives you high-level knowledge. It provides you a lot of links to external material to study.
https://acloud.guru/learn/aws-certified-devops-engineer-professional-2019
The closest you'll get without paying for the exam
The exam simulator is useful, as every question has answers and links to AWS documentation and blogs relative to the question.
https://acloud.guru/exam-simulator
I bought this e-course from Udemy and it is really good as Stephane demo the subjects hand-on. I also bought 2 other practice exams from Udemy and repeatedly take the exam and went through all incorrect answers to find out which area I need to improve.
Pass the AWS Certified DevOps Engineer Professional Certification (DOP-C01) with 20 hours of advanced hands-on videos.
https://www.udemy.com/course/aws-certified-devops-engineer-professional-hands-on
Over 375 Unique AWS Questions in 5 Practice Tests with Detailed Explanations, Reference Links, Score Tracking
https://www.udemy.com/course/aws-certified-devops-engineer-professional-practice-exams-/
AWS Certified DevOps: 1 high-fidelity 75-questions practice test: AWS Certified DevOps Engineer Professional DOP-C01.
https://www.udemy.com/course/aws-certified-devops-engineer-professional-practice-exam-dop
https://aws.amazon.com/blogs/apn/how-to-get-aws-certified-tips-from-a-devops-engineer/
Very useful...