I've tried the same thing, and get the same results. It appears that the systemd support is there, the cryptsetup support is ithere, but just cryptsetup-initramfs is not somehow there also.
It would be a shame to release bookworm with just the initramfs feature missing, when all the other pieces are there. Do you have any idea what might be blocking this? For what it is worth, dracut does work. -- micah