dragonxi we'll make an announcement when PHP 8.1 is available on our platform. There is no ETA for now.
If you're using PHP apps installed via our dashboard then you'll be able to set the version via the dashboard.
If you're using private PHP-FPM stacks then you'll need to make a lot of changes to your stacks to support the new version. We'll provide instructions for that once the new version is available.