Google warns that ADB backup and restore may be removed in a future Android release
 

ADB backup and restore is a handy tool that allows you to do more than some built-in backup options. You can save private data and installed applications without needing root, depending on whether or not the app allows it. Unfortunately, it looks like ADB backup and restore may be going away in a future Android release. A commit in AOSP is titled “Add deprecation warning to adb backup/restore.” A warning will be shown whenever the user runs the tool in the latest ADB tools release telling them that the feature might not stick around. A useful tool, and I’m sad to see it go.

https://www.osnews.com/story/130000/...droid-release/