configure the Agilex 5 FPGA using the Linux device tree

I have been stuck on a similar issue to this post (I am also using an Agilex 5 device):

Solved: Agilex 5 - configure FPGA from running linux via dt-overlay - Intel Community

I get to the end of the docs page as linked in the post above, and find this warning:

root@localhost:~# mkdir /sys/kernel/config/device-tree/overlays/0
root@localhost:~# echo overlay.dtb > /sys/kernel/config/device-tree/overlays/0/path
[  233.562309] OF: overlay: WARNING: memory leak will occur if overlay removed, property: /soc/base_fpga_region/firmware-name
[  233.573389] OF: overlay: WARNING: memory leak will occur if overlay removed, property: /soc/base_fpga_region/config-complete-timeout-us
root@localhost:~# 

I then execute the following:

rmdir /sys/kernel/config/device-tree/overlays/0
mkdir /sys/kernel/config/device-tree/overlays/0
scp host@192.168.1.1:/home/user/Desktop/GHRD/output_files/g_t_hps.core.rbf /lib/firmware/overlay.rbf
cd /lib/firmware/
echo overlay.dtb > /sys/kernel/config/device-tree/overlays/0/path

But there is no change in the LED pattern output on the board: i.e. the FPGA is not re-configured.

Could someone explain? Maybe I have misunderstood the flow for this?

Many thanks,

K