Is there any way to hide instruments per flow, instead of players - to reduce clutter in galley mode. For instance, say the Clarinet is in A in flows 1 and 4, and in Bb in 2 and 3.
No, there’s no way to do this. It has been requested a couple of times. Ultimately we need some kind of “focus on staves” or “staff sets” feature to help address this, which is something we’re considering for the future.
+1 for Focus on Staves feature