To set default apps in portal.office.com, sign into your account and access your app settings from the main dashboard. Once logged in, locate the settings menu by clicking on your profile icon in the upper right corner. From there, navigate to Settings > Apps. Choose the desired default app for opening files, such as Word, Excel, or PowerPoint. You can also manage other preferences for connected apps, setting which ones open specific file types. Customizing default apps in portal.office.com makes it easier to streamline your workflow by setting your preferred tools for document handling and collaboration.