Disclaimer: This guide is for educational purposes. Flashing custom ROMs can brick your device if done incorrectly. The author is not responsible for lost IMEI, dead SD cards, or nuclear war.
If you are still holding this device, you know the pain: a bloated TouchWiz UI, lagging multitasking, and apps that no longer support Android 6 or 8. There is only one solution to resurrect this phone: .
Join the "Samsung Galaxy A9 Pro (2016) Custom ROMs" Telegram or XDA group. Developers still push patches for the kernel sporadically. Keep your ROM updated to avoid the "Green Screen" bug caused by old GPU drivers.