Thanks Emily M. - I think I've done it, I copied everything into the Figma Kit" design file, on the Documentation page, then renamed it to "Just the homepage (wireframe)" and now have a "Home - no Mega" layer.
Additional Question if anyone is up for it, looking at the screenshot:
Do I make a change in "1" this change is automatically applied to everything in "2", which includes my layer in "3", and so stuff will change in "4" ?
(thanks for your patience)