Hello Christian,
Thanks very much for the interest in upgrading.
Yes -- Hauptwerk v5 is fully supported on macOS 10.15 'Catalina':
https://www.hauptwerk.com/requirements/
https://www.hauptwerk.com/wp-content/up ... isites.pdf
There are a small number of known compatibility issues with the platform, but they're minor (mainly cosmetic) and listed in the 'known issues' section at the end of the release notice:
https://www.hauptwerk.com/documentation/
(Hauptwerk v5 definitely won't run on OS X 10.10.x, but perhaps this thread might help if you want to try to upgrade your existing 2009 Mac Pro to a more recent version of macOS: viewtopic.php?f=16&t=17862 .)
I hope that helps.