This process is called a rollback , not an OTA downgrade. It requires a special "rollback package" that wipes all user data. It is not reversible via normal system updates.
: Ensure your device is currently on a stable realme UI 2.0 version (typically versions after C.05). How to Download the Rollback Package
If the local installation does not trigger, you can use the Recovery Mode method:
You forgot to wipe data after flashing. Fix: Force restart by holding Power + Volume Up for 20 seconds. Go back to Recovery > Wipe Data > Format Data > Reboot.