I have some news 
I found that we can indeed have page breaks when using theme-grid .
Form style needs to be set as “pages theme-grid”. Having “theme-grid” on its own doesn’t work.
(I know this is mentioned in the Enketo blog page that I have linked before but it was not clear to me, that it’s the combination of both “pages” and “theme-grid” that allows for page breaks).
Then, by default stand alone questions will be on their own page. Same for groups.
But we can nest groups in order to have multiple groups on each page, like this:
The result is great:
Btw, as you might have noticed on the above screenshot, once we break pages, the Navigation menu shows up:
