What I want to write is in 4/4 time: eighth-note, then dotted quarter-note tied to a quarter-note. Dorico writes this as an eighth-note tied to two quarter-notes, which isn’t what I want.
The global setting that regulates this case, I believe, is Notation Options > Note Grouping > Time signatures with half bars > Notes starting in the middle of the bar and crossing the half-bar. By default it’s set to Split at the first beat boundary. Try setting it to Split only at the half-bar.
If you want to force it on an individual basis then read up on Force Duration.
edit: middle of the bar, not bear. Notes starting g