https://stackoverflow.com/questions/18533567/how-to-extract-or-unpack-an-ab-file-android-backup-file

Install Android Backup Toolkit

wget https://downloads.sourceforge.net/project/adbextractor/android-backup-tookit-20180521.zip
unzip android-backup-tookit-20180521.zip
cd android-backup-tookit/android-backup-extractor/android-backup-extractor-20180521-bin

Unpack backup. Changes it from an ab to a tar file

java -jar abe.jar unpack ~/path/to/backup.ab ~/path/to/backup.tar

After thats complete, you can untar it. Change Desktop to the path you want to extract to.

tar -xvf ~/path/to/backup.tar -C ~/Desktop/