Unusual! Was this a fresh installation of the SDK, or are you migrating a project of some kind? I’m not certain why Composer would have delivered SDK V7 on a new project with PHP 8.1, that doesn’t make sense. You might run php -v from your shell just in case, perhaps, your environment is mistakenly invoking an outdated version of the PHP somewhere on the host. (Most likely Pesk upgraded your PHP runtime after the Composer install occurred, but it’s impossible to say.)
In any case, try running composer require auth0/auth0-php "^8.0". As a last resort, you can try manually setting the version in your composer.json file to ^8.0 and running composer install again.