btssn
This is not an osTicket issue, rather a hosting/setup issue. Your host should be able to enable a specific PHP version per site. There are many ways of accomplishing this however the most common way is via the Apache site config for each site. Ask your host to configure your “dolibarr” site to run PHP 7 and your osTicket site to run PHP 8. You will need to reach out to your hosting provider for further assistance. Let’s hope your host is sensible enough to enable such configuration or at the very least allows you to make such configuration. Good luck!
Cheers.