Unable to find headless.h in the github link while it is being generated by the TES the no-os guide explicitly asks not to use headless.c and headless.h files generated by the TES.
I don't think headless.h is required for No-OS build. Its an blank file. No-OS forum should be able to help more on this.
Moving to NO-OS subspace.
Please find the 'headless.c' in following git repo.
That's correct - headless.h is not required.
Retrieving data ...