After troubleshooting assistance from the Debian Printing team, I was advised to report my non-printing driverless printer issue upstream, which I have done.
https://github.com/OpenPrinting/cups-filters/issues/472 Given that driverless printing works in CUPS 2.4 (on Ubuntu 22.04) are they likely to fix 2.3.3 in Debian stable, rather than just suggest Debian updates cups[-filters/whatever] in stable? That is, assuming Canonical hasn't just fixed whatever the issue is in Ubuntu. Does anyone know if cups 2.4 in Debian testing is in a suitable state to consider (exceptionally) adding to stable? Alternatively, is it advisable to downgrade to a known-working version from Buster? Thanks, Gareth