Error in Galaxy tab a: 'Unable to restart your device. Verification failed' after supersu
Uhh, ok. If you're able to boot to TWRP, click mount and put a check mark in each box. Go back to TWRP file manager and poooof you shout see what you're looking for. Backup all partitions, then do a factory wipe.  Go to restore and only check "data". I suggest you root with Magisk (system-less) and find yourself a sweet custom ROM like AEX.