PHP compatibility issue between two different subdomains

I have two installations in two different directories, on a shared hosting space. One is Drupal-based and one is your standard WordPress blog. The first one is quite old, and only runs on **PHP 5.3** (I wasn't able to update it further than Drupal 6.38 without losing contents).

This wouldn't be an issue, if it didn't prevent me to run WP (version 6.0) on a PHP version newer than **7.3** (like **8.1**), because in that case the other website would fail to load (error: _Not Implemented - GET not supported for current URL_).

The only way the two can coexist is apparently having **PHP 7.3** as a global setting, and **5.3** for the Drupal subdomain. If I try to set a _.ohvconfig_ file with PHP 7. 6 or newer in the WP directory, WP goes down.

Is there something I can do to have both of my websites to run on the newest PHP version they can manage?