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?