I was using this, too, and I was disappointed to discover that it had been removed.
In macOS 10.14, cupsfilter invoked an XHTML/HTML to PDF filter program, /usr/libexec/cups/filter/xhtmltopdf, as listed in the MIME conversions file, /usr/share/cups/mime/apple.convs:
application/xhtml+xml application/pdf 33 xhtmltopdf
text/html application/pdf 33 xhtmltopdf
macOS 10.15 has neither the xhtmltopdf program nor the entries above; I assume Apple meant to remove them, but I don’t know why.
As a workaround for private use, xhtmltopdf from the macOS 10.14 installation package does seem to be able to run on macOS 10.15.4. The file is very small (only 31 K), so clearly most of the work is done by the system frameworks with which it’s dynamically linked.
The xhtmltopdf filter isn’t part of the open-source CUPS package, but the filter(7) manual page does give some hints on how to invoke it. For example, at the most basic, you can run:
./xhtmltopdf 1 "" "" 1 "" input.html > output.pdf
To suppress the “ERROR: Unable to open PPD file” message, set the PPD environment variable to point to a generic one:
PPD=/System/Library/Frameworks/ApplicationServices.framework/Versions/A/Frameworks/PrintCore.framework/Resources/Generic.ppd \
./xhtmltopdf 1 "" "" 1 "" input.html > output.pdf
You can also specify options, as with the -o flag to cupsfilter; for example, to change the page size to A4:
PPD=/System/Library/Frameworks/ApplicationServices.framework/Versions/A/Frameworks/PrintCore.framework/Resources/Generic.ppd \
./xhtmltopdf 1 "" "" 1 "media=A4" input.html > output.pdf