Thanks, michael, you pushed me in the right direction 🙂
Most of the installed HP utilities use python3 which has the cupsext extension installed.
hp-doctor and the filter however use the system default which is python2. Python2 does not have the extension.
So I did (as root):
nano /usr/lib/cups/filter/hpps
and changed the first line from
#!/usr/bin/env python
to
#!/usr/bin/env python3
(notice the '3' at the end)
Now, printing seems to work (test page, kate).
So we found the reason, but questions are remaining:
- my solution is just a quick hack - what could be the correct solution?
- who is in charge of fixing? HP or the packager of HPLIP?