Thank you, ssmith. However there were only TWO dots at the bottom of the screen that appears after tap’n’hold.
(I had four home screens arranged as I chose)
That second one shows what I learned is called The Library - about 8 or ten bubbles each with several of my apps as icons in each of them. The bubbles are labeled by Apple’s categories. (And that a tap yields a simple and inclusive list of all apps on my phone.
it turns out that the answer is in SETTINGS/FOCUS/PERSONAL/HOME SCREEN/CUSTOM PAGES/where my lost (hidden) Home Screens are now called Pages. Each can be ‘activated’ by tapping the circle beneath each one.
it took me a LONG time to discover it, because I had never used/changed the default state of FOCUS. I had read about it a few months ago but decided I didn’t need its capabilities, so I definitely never activated any Focus setting.
Thanks again – and given your thoughtful response to my plea, I urge you to find+cite the Apple Support instruction which worked for me, in addition to the ‘standard’ one you referred to.