There were a few bugs upgrading emacs-addon packages to bookworm (e.g. #1040690). The symptom is that the elpa/foo-$version directory created by the installation was not removed correctly on package removal.
I have uploaded to experimental a new version of dh-elpa (last is 2.1.1) meant to address these bugs (but only in newly created packages). Unfortunately this represents a step backwards design-wise, as it seems that in postrm scripts, we cannot depend on our dependencies being installed. For this reason it is crucial that the emacsen-removal scripts (which are now embedded, rather then calling a script from dh-elpa-helpers) are correct. I would appreciate any feedback (or even ideas for better approaches). Rob and I talked about this a fair amount, but maybe someone else sees a way to avoid emedding the (body of the) removal scripts in the dh-elpa built packages. In any case, please rebuild a couple of your packages and examine the output, e.g. with piuparts. This is a case where just testing buildability (e.g. with ratt) is insufficient; the real question is do the resulting packages install and remove cleanly.