Found the issue, kpmcore is 24.01.80 is broken, upstream added a few commits to fix the changes, but I decided to just revert the breaking commit:
https://invent.kde.org/system/kpmcore/-/commit/6e7efe97c29c4bdab38388a6931df379dd2a8d3b
You can test in live mode:
sudo pacman -U http://kaosx.tk/repo/kde-next/kpmcore-24.01.80-3-x86_64.pkg.tar.zst http://kaosx.tk/repo/kde-next/kpmcore-debug-24.01.80-3-x86_64.pkg.tar.zst
and run the installer (or open the partitionmanager and create a fat32 512Mb EFI partition).