In supporting Typemarker, I had a ticket reporting of the PDF file not being attached to report emails. After investigation, I was also able to reproduce the same behavior when the Typemarker plugin was not running alongside Pro Reports. At the time, my site was running PHP 8.0. After switching to PHP 7.4 the PDF is properly generated and attached to the outgoing email.
It would seem that the Pro Reports extension may not yet be fully compatible with PHP 8.0. Is anyone else able to reproduce or confirm this?