libgtk-3-0 used to ship the following print backends in debian buster
and debian bullseye:

libprintbackend-cloudprint.so
libprintbackend-cups.so
libprintbackend-file.so
libprintbackend-lpr.so
libprintbackend-test.so

By default only cups and file were enabled.

Debian bookworm only ships

libprintbackend-cups.so
libprintbackend-file.so

probably due to the bug-report
https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1025271

Please re-enable the other print backends in the next build.
If some undesired backends are available by default, this can be
configured in the file
/etc/gtk-3.0/settings.ini

The stanza there should look like (for previous debian defaults):

[Settings]
gtk-print-backends=file,cups

So the correct fix for #1025271 is to leave all print backends enabled
and add a debian-provided config-file with the enabled backends unless
there is another way to set a default config in recent gtk.

The current state of affairs makes debian bookworm unuseable for people
with other print backends like lpr. This is needed, e.g., for the
debian-provided lprng package. It is also needed for printers that
support the lpr protocol natively.

Note: I've searched if the other backends are available in another
package now, this does not seem to be the case.