But if I try to input a note, say to add a note to the chord, the note value changes to a single dotted note, which is different from other note values.
When I edit that on Windows 11 Por with Dorico 6 it works fine.
I cannot imagine there is any engraving or notation option that affects this.
Just sometimes, rarely, but can happen, you need to delete the notes and enter them again. Not scientific, but can work. It’s happened to me a couple of times.
I had never noticed that, but it looks like if you select the note, then press Enter or Shift+N, the value remains as a double-dotted quarter, but if you directly double-click the note, then it becomes a single-dotted quarter, indeed.
Same for me in another file, with or without Force Duration (i.e. with or without the Notation option allowing double-dotted notes).
I never use double click. But yes, when I do, it mucks up, with a single dot. So I can confirm that behaviour. That’s got to be wrong. Can that be classed as a bug? Reluctant to ever call anything a bug at this, but this looks like one.