Migrate LMS PHP 5.5→8.5

I need help bringing a large, legacy learning-management system—well over 50,000 lines of plain PHP 5.5—up to PHP 8.5. The application was written without any framework, and there are currently no automated... (Budget: $1500 - $3000 AUD, Jobs: JavaScript, MySQL, PHP, PHPUnit, Software Architecture, Software Development, Software Testing, Web Development)