Another way you can customize your SharePoint Online environment is through the use of tools such as Microsoft Flow, Power Apps, and Forms. SharePoint Designer 2013 is a tool that's used to develop and maintain sites, applications, and workflows in classic SharePoint and SharePoint Server. While it is no longer under development, it is still supported from the aspect of being used to create and maintain classic SharePoint site experiences, including workflow automation and integration with content sources.
However, Microsoft now recommends using a combination of Microsoft Flow, Forms, and PowerApps to replace features and functionality found in SharePoint Designer 2013 and InfoPath Services.
Microsoft has renamed Flow to Power Automate, so these terms may be used interchangeably. Depending on when you take the MS-300 exam, the content may reference either product name.