The non-Ultimate HL product on DTRPG lists Dungeons & Dragons as well as Pathfinder OGL 1E as the compatible Rules Systems - which to me sounds like 2 different systems, and they just neglected to specify which edition of D&D, though since it was published during the 5e era, it seems apparent that they mean 5e, especially since
they have official 5e content for SOP on DTRPG in addition to Pathfinder. Since the HL files on DTRPG list 2 rules systems, I'm just inferring that it was intentional - but again, I'm probably wrong and that was an oversight. However, for a brief window, I was able to open up a DDS SoP file within 5e's Editor when I had changed the download folder to 5e - but no unofficial HL 5e content would load at all until I completely uninstalled all of it.