I couldn’t find any post for encrypted boot on same device.
So far I tried your guide and it works with a detached usb, no problem. So I tried to create three partitions (EFI, boot, root) and then follow all the steps (basically same guide but without header partition, and with “/” on a partition instead of a device on its own).
This always leads to this error before creating the keyfiles:
mount: /boot: can't find UUID=<some_uuid>
And that uuid is nothing of value, as uuidB and uuidR are different.
The same kind of error is shown again when I try to boot qubes.
I don’t understand why the process works for detached boot but not on the same device.