Sharing a workaround: Found a way to write polyrhythms with the proper time signature displaying.

Space does not enter rests; it advances through them. Turn on rest entry and force duration and tap either a note name or the letter Y. That will input rests.

Ah! As usual, excellent - thanks so much. Now, where would I have found that in the help files/manual; it was entering Y that did it, and that’s not mentioned there. This forum is brilliant - but I’ve never needed a forum as much; in fact, I can’t think of any other software I use where I’ve needed a forum at all. I know Daniel’s said they are aware that the documentation needs updating - I do hope they consider some of the topics here, since that gives a strong clue about what users need help with.
Despite that small rant-ette of frustration, I am beginning to get used to Dorico; there are certainly a lot of things I like about it.
Anyway, this is getting off-topic now, so I’ll try to disappear for a while.

Well though it’s out of date and thus doesn’t mention Y, it still mentions using note names rather using space.

Dear piano888,
The documentation in the Version History is really accurate and remarkable. I suggest you try there too.

Thanks to both. I’ll follow those up. I did think I’d done - or attempted - a ‘positive’ rest entry, so will have another go later.