@sgunhouse --- yea, sorry, incorrect answer. Not an option there.
You should be able to right-click on one of the dividers like 'Today' and there would be a context option to not display in groups, but it is missing.
As I was writing this, I found the context menu I needed...
I had to collapse the groups and r-click in the blank space and finally found the group-by menu..
4 other browsers on this particular machine, and they are all fine.
Opera and Opera GX, not so much, but, problem now solved.