TWRP says "Failed to mount /data" or "/sdcard". Solution: In TWRP: Wipe → Format Data → type yes . Then reboot recovery.
Ultimately, the argument for installing TWRP on the Samsung Galaxy Tab 3 GT-P5210 is an argument against planned obsolescence. In a world where electronics are increasingly treated as disposable, the ability to overwrite the manufacturer's limitations is a powerful form of agency. TWRP does not just make the tablet "better" in terms of speed or software version; it fundamentally changes the relationship between the user and the device. It proves that with the right software, a decade-old tablet can still find relevance in the modern world, proving that value is defined not by a release date, but by the freedom to modify.