Dear @Hangman, @Alfred,
Thank you for your notes and much appreciate the quick response!
My hope is that Serif would fix this bug in Publisher, as both Affinity Photo and Designer work correctly with US Extended.
Very long ago I had decided to use US International (Windows) and US Extended (MacOS), as those remain the closest relatives and I was stuck with Windows at work. I made a keyboard layout on the Mac that extended the US Extended layout and has worked very well for me.
@Alfred - there are layouts on the Mac that use AltGr, but the Mac and the Windows layouts for some of the alternative keys are different, so is the layout for other localised keyboards. Hence the decision to use a US layout, which is always the same, available on all platforms. Oh, and greetings from the (momentarily) sunny Firth of Clyde!
@Hangman - composite entry with the UK layout does indeed work, so it is clearly a bug with the US Extended layout.
In any case, the point is that Publisher needs fixing! I have been using InDesign and considering Publisher as the long term solution. I understand that it is a younger product, although Serif has a long history. I was wondering what is your view on bugfixes? Is there a good chance?