click the Start Using Profiles button. If you already have a profile or two set up, click the + button in the bottom-left ...

A new "multiuser" widget has been added in Android 16 that lets you quickly switch between users on your device.

Then, toggle the Automatic profile switching button to turn it on. However, if it is already turned, there is no need to follow this step. In that case, you can follow the next step. Once done ...