Please remove the i386 binaries of diffpdf.  Since 1:1.0.6-1 it is
built from disparPDF, which needs the Qt 6 binding of Poppler, and
poppler does not build libpoppler-qt6-dev on i386 (since 24.02.0-5).

Because diffpdf is now a transitional package, there actually aren't
any i386 packages to be removed from Unstable. There are no apparent
blockers to diffpdf migrating to Testing except waiting a few more
days:

https://tracker.debian.org/pkg/diffpdf

Thank you,
Jeremy Bícha