Expected Platform Developer I Exam Topics, as suggested by Salesforce :

• Module 1: Developer Fundamentals: This section of the exam covers the understanding of multi-tenant concepts and developing models like the MVC architecture and Lightning Component Model. It also covers pinpointing common use cases and the most effective strategies for declarative versus programmatic customizations.
• Module 2: Process Automation and Logic: This section of the exam covers the identification of the declarative process automation capabilities and how to declare methods, variables, and modifiers. It also covers utilizing Apex control flow statements and writing SOSL and DML statements.
• Module 3: User Interface: Inside a particular scenario, this part of the exam covers displaying or editing content related to Salesforce data with the Visualforce page feature. It also covers explaining the Lightning Component Framework, its advantages, and what content can be used with a Lightning web component. It covers showing and utilizing a customized interface component such as Flow and Visualforce.
• Module 4: Testing, Debugging, and Deployment: This section covers writing and performing tests related to triggers, classes, and processes by utilizing different test information sources. Moreover, it covers the understanding of various Salesforce Developer Tools such as CLI, DX, and Developer Console.