Please provide python3-poppler-qt6. According to
https://endoflife.date/qt, Qt 5.15 has no support since May 2023, only
Qt 6 versions are maintained. So this is probably the same for libs like
poppler-qt which depend on Qt.
It seems Debian already has the package "libpoppler-qt6-3" but not yet
the corresponding python package.

This is not going to happen. Upstream has given up delvelopment in
favour of QtPdf.

Dear submitter,

as the package python-poppler-qt5 has just been removed from the Debian archive
unstable we hereby close the associated bug reports.  We are sorry
that we couldn't deal with your issue properly.

For details on the removal, please see https://bugs.debian.org/1141366

The version of this package that was in Debian prior to this removal
can still be found using https://snapshot.debian.org/.

Please note that the changes have been done on the master archive and
will not propagate to any mirrors until the next dinstall run at the
earliest.

This message was generated automatically; if you believe that there is
a problem with it please contact the archive administrators by mailing
ftpmaster@ftp-master.debian.org.

Debian distribution maintenance software
pp.
Thorsten Alteholz (the ftpmaster behind the curtain)