Another KB5048652 update screwup?

Officially, nope.

Unofficially, despite exhausting Logitech tech resources I have inadvertently solved the issue.

I tried the keyboard on another pc, as reqd.  I had to drag the box out and fumble about down the back to unplug it, where it had been connected since the pc was new about 5 years ago.  On restoring the keyboard after determining it was fully functioning, I plugged it into the desktop hub rather than struggling to drag the pc all out again.  Hey presto full functionality instantly restored.

Why simply changing the usb socket used had this result I haven't a clue. its worked flawlessly, untouched for several years until this kb fix but in researching this issue I found several comments about similar odd hardware and assorted failures.  Whether they were usb connected i dont recall or wasn't stated but hey Its worth a try jiggling your usb devices about!!