Creating a custom dtb for imx6 Colibri...

I am trying to create a custom dtb for a Colibri board. I have been unable to figure out the exact steps to create a dtb from a dts in the build environment.
To try and understand what might be wrong, I tried to follow the step on this webpage:

specifically " Customizing Nodes and Properties" and " Choosing the Base Device Tree".
When I follow these instructions to what appears to be a very simple example and hit step #4, “make dtbs”, I get an error:

Any idea about what I might be doing wrong?
(Note: I have previously performed a successful “bitbake tdx-reference-minimal-image” in this environment so I believe that my build configuration is good in general).

Thanks in advance.

Colibri iMX6DL 512MB V1.1A, 1.1Y
Colibri Eval Board Rev 3.2
Linux BSP 6.x (in process of migrating)

You need to follow these instructions - Build Linux Kernel from Source Code | Toradex Developer Center. And you should build a Linux kernel before building the Device Tree.