Based on my understanding, Azure App Service supports PHP version 8.3 already. See the below Url that shows the supported PHP versions.
https://github.com/Azure/app-service-linux-docs/blob/master/Runtime_Support/php_support.md#php-8
You can check the runtimes from the CLI command. I just ran the command and it shows the available versions, and it include 8.3
You can sent the php version by the CLI command
Hope this helps