Instructions apply tosmartphonesandtabletswith Android 4.4 KitKat or later.
One free option is the Fullscreen Immersive app from PhotoSafe.
The free version of the app has a few bugs.

For example, hiding the navigation bar may prevent you from using the on-screen keyboard on some devices.
Download the PhotoSafe Fullscreen Immersive app from theGoogle Play Store.
Similar paid apps, likeImmersive Mode Manager, are available for free with Google Play Pass.

Launch the app and tapI Agree.
Tap theOfftoggle in the top-right corner to turn itOn.
Tap theAllow permissiontoggle, then tapback.

Individual app preferences will override the option you choose at the top of the screen.
Keep in mind that these configs don’t affect apps that run in Immersive Mode by default.
As of Android 10, there is no way to turn off Immersive Mode for all apps.

Launch the PhotoSafe Fullscreen Immersive app and tapUsage Access.
TapFull Screen Immersive Mode.
TapAllow usage tracking, then tapbacktwice.

All of your apps will appear in the bottom part of the screen.
Tap themagnifying glassto search your apps.
Enter the name of the app.

Tap the app to set your preferences:
What Is Immersive Mode?
Thestatus bardisplays the time, notifications, and other important information at the top of the screen.