To get your Microsoft 365 tasks on the go, you can use the Microsoft To Do app for Android or iOS. Just sign in using the same Microsoft account that you use with Outlook and your tasks will automatically sync between To Do and Outlook.
To Do also supports flagged email as tasks, so you can easily add and manage tasks from your Outlook inbox on mobile. Please know, though, that you'll first need to enable the Flagged Email list on desktop in the To Do web or Windows apps. Just select the option to Show List when prompted or turn on the Flagged Email list setting.
Note: For iOS only: If you have tasks created on Outlook for Windows, Outlook for Mac, Outlook on the web, or Microsoft To Do, you will see the top 3 tasks from your default task list in your Outlook for iOS search home page for your default mail account. You can mark them as complete or tap on a task to do more in Microsoft To Do.