Thanks Netstruggler
I did discover a previously unknown setting had been changed by an update and I guess I shall see whether it's the culprit. Meanwhile the following link may be useful to anybody suffering from the same Windows 10/11 malaise. Under Systems>Power and battery. system recommendations> at the bottom of the list you will see a contrarian setting of "Put my system to sleep after 10 minutes" This can be changed to "NEVER" by motoring to the bottom of a long list. It obviously overrides the basic setting (found Static elsewhere) of "NEVER" (on sleep). Microsoft needs to get their excrement in one pile. So much for Win 11 - need now to check Win10
The more complex link. I found Event Viewer to be too intricate to navigate for a novitiate of only 30 years of Windows.
https://tinyurl.com/2wcjuedz None of my ancient laptops will hibernate. There is no provision for doing so. I inherit my hardware from my son who abandons his gear as soon as something new rears its head.