Samsung is taking a bit too much time to release OneUI 7 for the older phones but xdaforums is here to rescue. One developer has released a GYA2 stock firmware that fetches and installs the official One UI 7 firmware on to your S21 Ultra.
Keep in mind that once you’ve installed it, you will loose warranty on your S21 Ultra as this is a third party ROM. However, you can simply flash stock ROM again to regain the warranty. How to install:
- Download GYA2 Stock FW for your S21 Ultra device
- Reboot to ODIN and flash stock
- Wait for boot after flash
- Reboot to recovery – custom recoveries are not supported, so S21 Ultra TWRP will not let you flash this ROM.
- Locate menu Apply update from ADB using the volume keys and select it with the power key
- On your computer open a cmd window (make sure that you got ADB tools installed) and write adb.exe sideload PATHTOUPDATE.BIN and press enter
- After a successful flash it will auto reboot to One UI 7.
There you have it. You’ve successfully installed OneUI 7 ROM onto your Samsung Galaxy S21 Ultra.