This is correct. The content moved to a partition when earlier boot stages began to need access to the tree for support of secure booting. U-Boot has ext4 filesystem drivers, so U-Boot can read the rootfs, but those earlier stages lack ext4 drivers. Earlier releases did not require this, but those releases did not need early access to the tree.
This is a yes/no question, please clarify -
R32.3.1 Does /boot/extlinux/extlinux.conf support FDT?
No (there are a couple of parameters which might work here, but most do not; all parameters which do work here can also be put in the “chosen”/“bootcmd” entry of the device tree).