Since this phone is older, support has tapered off, and some bugs remain:
OPPO Team
The does not officially support the ColorOS 12 (Android 12) update . According to official OPPO Community support, the device reached its "end of life" for major software upgrades after receiving its final promised update, ColorOS 11.1 (Android 11), in 2021. Why the OPPO A9 2020 Will Not Receive ColorOS 12 oppo a9 2020 coloros 12 update
: Uninstall unused apps and use the "Force Stop" feature for apps you rarely use to free up RAM. Since this phone is older, support has tapered