In fact, whatever I do, I end up with this. I tried e.g. selecting the next barline, inputting the same thing, which then generates what I want in the second bar, and then deleting the first bar: then the correct pickup is left only in the lower staff! What am I doing wrong? Honestly, I seem to be following the docs here…
edit: the behaviour persists with “4/4,1”: the pickup only materializes in the lower staff.
If you click a time signature in a score, all vertical instances should be highlighted.
If they are not, there are local time signatures “lurking around”. If I can select individual (=local) time signatures I’ll just delete them until everything is clear - and re-enter the main time signature. These oddities happen a lot when having used xml import.
The method of @charles_piano is working too, but you have to know what you are doing.