I really want the first ending to play from the start of bar 21. But if I put (or drag) the Segno inside the repeat - say to the first note (not shown in this extract grab) of bar 21, Dorico jumps all the way back to the very beginning (Bar 1) of the Flow.
Secondly, do I actually need a ‘Fine’: if so where? I’d have thought at barline 28. But that too seems to mess up which repeat plays when… if at all.
Maybe a fluke: is there a known issue (Dorico 5.1.81.2225 on 15.4.1) with improperly-formed Repeats (like these of mine here) where the Cmnd + G shortcut does display the dialogue box, but fails actually to jump to the bar I want when clicking ‘OK’?
DS al Fine will jump back to the segno, then carry on until it reaches a Fine at which point it will stop. This is used where you want to repeat some, but not all, the material.
If you want to jump back and then play through to the end, just use a DS (with no Fine).
Nesting a DS jump inside a repeat could be illogical (in which case Dorico may refuse to obey!)