I want to downgrade macOS Ventura beta to stable macOS Ventura

FWIW, the last beta, 13.0 RC2 and the release version are one and the same so there's no point in downgrading. If you don't wish to receive further beta versions just unenroll and wait for the next stable release.

You should have been offered the final release of Ventura during the last days of the beta.

Don't install any future updates and you should have the current released version.

I've never seen any of the beta releases be unstable.

Unenroll Your Devices

How do I restore a prior release of macOS?

To go back to a prior release of macOS, you can follow the steps here:

Restore Shipping Software