I followed this - https://www.rapiddg.com/article/creating-custom-layouts-layout-paragraph...
But there's some typos:
The template file should be "layout--fourcol.html.twig" rather than "layout--fourcol.twig.html".
Also "gh_display" in the full entry example for the layouts.yml should be "custom_layouts".
More examples can be found in the "Layout Discovery" module within core.