advanced ISO options no longer showing up (bullseye, lb 20210407)

I have a custom live distribution I was building for buster that included, for both the BIOS and EFI ISO menus, various custom options by specifying them in includes.binary (see https://github.com/mmguero/deblive/tree/master/bullseye/config/includes.binary), using "isolinux/advanced.cfg" and "boot/grub/grub.cfg" for BIOS and EFI, respectively. This all worked correctly when building with lb under buster. When the ISO would boot, choosing the advanced options menu would show my custom entries.

I've since updated everything to bullseye. While I've gotten the various expected update-related issues taken care of (new package versions, other minor tweaks) and the ISO builds fine now, my custom entries no longer appear (see https://github.com/mmguero/deblive/blob/master/build.sh#L111-L147) for my build process.

I'm assuming there's some recent change I just need to account for, files that need to live somewhere else now, but I'm not sure what. If anybody has any ideas I'd appreciate them.

-SG