This is the first release with qt5 support.
Created attachment 434990 [details, diff] hplip-3.16.5.ebuild.diff Possible necessary changes. I bumped EAPI to 6 and added qt5 support but did _not_ test it as I still have USE="-qt5" on my dev machine.
Lars thanks for your work. However I was already working on it with almost the same changes plus some additional modifications. I will add this in the next days.
Fixed in Git. Thanks for the report.