Hi, congrats for solving this long standing problem.
A few years ago this would have been great news for Knoppix, which staid for quite a while with SYSLINUX for EFI. But somewhere between versions 8.6 (2019) and 9.3 (2022) it switched to GRUB. Although the most recent commit on https://repo.or.cz/syslinux.git is 4.5 years old, consider to post your patches to sysli...@syslinux.org Maybe it helps some puzzled SYSLINUX user in the future. Have a nice day :) Thomas