I believe this is the bug in raspi-firmware: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1032186
(For anyone interested, the code change to fix it is here: Don't copy files to /boot/firmware on remove (Closes: #1032186) (7ebd5e57) · Commits · Debian / raspi-firmware · GitLab)
This was fixed in raspi-firmware 1.20230405+ds-1, so it has been fixed in unstable and testing. However, Debian stable has raspi-firmware 1.20220830+ds-1, and I don’t see any bugfix updates for it.
So I would recommend that we request to the raspi-firmware maintainers to see if the fix can be applied to raspi-firmware in Debian stable. I see they have a mailing list here: Pkg-raspi-maintainers Info Page