Before starting on your quest to become an Azure DevOps engineer, you should know about the path! You cannot just qualify as a DevOps engineer expert just by qualifying one certification. Candidates should note that they need to have a clear idea about the fundamentals of Azure. You have two possible scenarios in which you can apply for the DevOps engineer expert certification from Azure.
A candidate should have an associate-level certification either as an Azure administrator or Azure developer. So, if you are new to the Azure learning path, then opt for the Microsoft Azure Fundamentals exam i.e. AZ-900 exam preparation first. Then, you can proceed towards an associate-level Azure certification as Azure Administrator or Azure Developer.
The Microsoft Azure administrator associate certification exam has the title AZ-103 while the Microsoft Azure Developer Associate certification exam has the title AZ-203. You can choose either one of them for obtaining eligibility to appear for the Azure DevOps certification AZ-400 exam.
You can find more details here:-
https://www.microsoft.com/en-us/learning/azure-devops.aspx
For the preparation of Microsoft Azure DevOps Solutions certification, JustCerts is an ideal choice
https://www.justcerts.com/microsoft/az-400-practice-questions.html
Hopefully, you got your answer in detail.