I'm finding on a MacBook Pro M1 that never closing NX Studio cuts down on the lengthy scanning and the spinning wheel of death. Drop NXS to the dock with the yellow button but never click the red button.
When first starting NX Studio if it doesn't start promptly walk away and do something else. As watched water never boils, NX Studio never starts. 
Hope this helps,
Dave
I can see how it would speed up use if it is allowed to be on the background all the time, but it'll consume resources while it is going through the files. In my opinion the software has no business looking into other directories when asked to view a specific directory, and Nikon should change this behavior.
Currently I'm using LRC as my main editing tool mainly because of the enormous waiting times NX Studio sometimes asks me to wait for, and I only use NX Studio when I need a specific feature which is not available elsewhere. This wouldn't have to be so, as I prefer Nikon's raw processing style.
Anyway, thanks for the tip on leaving the software running while not being used, to make waiting times shorter when being used. I use Windows but I suspect it'll be a similar story there. I recently got 32-> 48 GB RAM upgrade as one of my RAM circuits developed errors and causes software crashes, and I ended up increasing the amount of total memory in the process, which strangely enough has made editing smoother even though it is never even close to using all the memory available.