> ^ surprised by this line. guess it also impacts lib32 packages on amd64
The reason for this is that in Debian, package name and ABI are coupled, as that allows you to coinstall multiple versions of libraries with different ABIs. This transition changes the ABI on 32-bit architectures, so the package name of impacted packages also has to change (they get a "t64" suffix). While it's technically possible to have different package names on different architectures, that's a PITA to deal with, so they opted to also change the package names on 64-bit architectures, where it's not strictly required.
The reason for this is that in Debian, package name and ABI are coupled, as that allows you to coinstall multiple versions of libraries with different ABIs. This transition changes the ABI on 32-bit architectures, so the package name of impacted packages also has to change (they get a "t64" suffix). While it's technically possible to have different package names on different architectures, that's a PITA to deal with, so they opted to also change the package names on 64-bit architectures, where it's not strictly required.