I’d like to display bar 4 stretched out to show fingering details etc. in the trill.
How can I get bar 4 clipped, stretched, and isolated in the frame below the main content?
You can’t isolate a specific bar in a music frame: they always start at the start of the flow.
Alternatively, copy bar 4 into a separate flow and show that in this music frame. You can set the flow to show a normal barline at its end in Notation Options.
Or, create an ossia staff within your existing flow?