Re: print/cups-filters, print/libcupsfilters and print/libppd

I found your questions to be good ones, as with regard to the twisty
maze of CUPS components, all alike, many others have the same sorts of
feelings (to blur adventure and eliza).

See

  /usr/pkg/share/doc/libppd/README.md

which is likely to be helpful in beginning to understand.

The basic point is that PPDs are now the old way, and there is some new
"Printer Applications" thing which is

  emulations of driverless IPP printers, provides printer properties on
  `get-printer-attributes` IPP request


And

  PPD file support is going away in CUPS 3.x, to be released end-2023.

however it was actually released in January of 2026.