"; No XSLT processor found

Oh boy, this is bad. Stop the press! You REALLY need a XSLT processor do make all this stuff here works. Let me explain why.

All the idea of PHPReports is based on transform XML data on something else.

On a first moment, it transforms your XML layout file (that one you put your FIELDS etc) in PHP code that uses the PHP classes provided on the package to create another XML file with all your report data inside of it, and transform it again using an output plugin to the format you choose.

I can see that you're using PHP 8.
With this version is recommended to use the PHP XSL extension, and it's very easy to configure.

I can see that you're running GNU/Linux, so you'll have no problems with this. ;-)