Samsung might have made the Galaxy Tab 7.7 stuck at Android ICS but that has not stopped the folks at XDA from churning out Galaxy Tab 7.7 Marshmallow android 6 ROMs. Here is how to flash android 6 for P6800 Samsung Galaxy Tab 7.7.
1. Latest TWRP for Galaxy Tab 7.7 (2.8.6.x or above) is required.
2. Download ROM (+Gapps (+SuperSU)) and copy to the SD card (external or internal – if you want gapps and root of course. Or you can root Galaxy Tab 7.7 later.
3. Backup data to external sd and keep in a safe place
4. Reboot to recovery (Press [PWR] + [Vol+], Release [PWR] when Samsung Logo appear)
5. Factory reset / wipe data
6. Flash ROM (+Gapps and SuperSU if you want to ROOT)
7. Reboot and wait for at least 10min. (Block mode not working for all devices. It might take longer for post setup).
How to enable "Developer options" in Settings?
1. Settings > About Tablet
2. Hit "Build number" 7 times
To restore the default state (Developer options hiding):
1. Settings > Apps
2. Select the app "Settings"
3. Hit "Storage"
4. Hit "CLEAR DATA"