The Hestia control panel differs from its Vesta counterpart by having a PHP version selector. The user can manually choose one from 5.6, 7.0, 7.1, 7.2, 7.3, 7.4, 8.0, 8.1. A separate PHP version can be set for each user’s site: the current version will be used by default.
To change it, you need to click on “Edit Domain” in the WEB section, then — “Advanced Options”. You should select the desired version in the “Backend PHP-FPM Template” line and save the settings.
The phpinfo.php script will help you find out if the changes have been applied.