LFS chroot cannot find /usr/bin/env
I found the problem! It was a bad symlink (/lib64/ld-linux-x86-64.so.2 pointed to the absolute path on the host system, not relative to the LFS root, /lib/ld-2.36.so). It is such a shame that chroot gave me such a misleading and vague error message, instead of clarifying what and where went wrong. I changed the link, and now it works perfectly fine.