The steps to do soo are not hard tho.
You just need the android 13 firmware this one: https://oxygenos.oneplus.net/8173_sign_LE2111_11_F_OTA_2290_all_nRBuNP_00011011.zip
Then enable developers options by tapping "Build Number" 7 times
Enable Usb debugging in the developers options.
Then go to About device > Up to date, 3 dots on the top right and click local install.
Then select downgrade firmware, Extract > Upgrade
If the local install button is greyd out just follow the steps in this guide: https://droidwin.com/local-install-greyed-out-in-oneplus-how-to-fix/