This is a stupid question, and I’m sure I’m missing something obvious here. When I write three quarter-notes in a 6/8 bar, I almost never want the middle note tied over the half bar. Is there a note grouping setting I’m missing that will do this automatically without needing force duration or hidden meter changes?
No, you’ll have to use either force duration or a hidden meter change to do this. It might be nice if Dorico “knows” that three quarters in 6/8 should be written as such, but it also goes against the metrical rules of 6/8. Kind of a tricky question!
It is indeed technically “wrong,” but the 6/8-3/4 relationship is so common that it often warrants an exception to the rule (not always, but often enough). Same goes for two dotted quarters in 3/4. This would be a useful notation option to add in a future update.