Inherited an CI project and am pretty lost with it.

Version can be found in system/core/codeigniter.php (const CI_VERSION), there it will list the version number or use echo CI_VERSION;

Edit: If HMVC is used (you can see this probably in the third_party folder which should contain an MX directory)
As for HMVC (probably of WireDesignz), this is not compatible (see the pull requests on howto fix some of the issues).
But for PHP7.3 you could use https://github.com/N3Cr0N/CodeIgniter-HMVC instead of https://bitbucket.org/wiredesignz/codeig...sions-hmvc (which is not supported anymore ?)