Where in the PrusaSlicer settings can I disable the blue layer shown in the picture?  

RE: Where in the PrusaSlicer settings can I disable the blue layer shown in the picture?

I think the image is made from the screen with the print preview? Correct? 
if so, the colours are explained in the feature panel (set prusaslicer to expert mode and in the panel choose feature type. )
You will see the blue line is : "Overhang perimeter". 
All lines, to be printed, what are not supported by other material are called "overhangs" (like a bridge). 
Such a overhang needs support to  be printed. 
In your image the supports are set nicely (the darkgreen material). 
This supports the overhang. 
So this blue line cannot be removed, it is just a signal to the user. 

RE: Where in the PrusaSlicer settings can I disable the blue layer shown in the picture?

It can be removed.  Its not a 'layer though'.   Its bridging as indicated by the key as Eef mentioned.  Print Settings>Layers and Perimeters>Quality>Detect Bridging Perimeters.  Its a Yellow setting so you must be in Advanced or Expert modes to see it.

When its turned on the slicer will detect bridging perimeters and as such any that meet its criteria will be detected and print them with bridging settings, ie increased fan, slower print speeds, using bridging flow etc.  When that setting is turned off it uses normal perimeter/external perimeter settings.  

You can still use support if needed.  

RE: Where in the PrusaSlicer settings can I disable the blue layer shown in the picture?

Thank you. This is what I was looking for. Best regards and I wish you lots of good energy. 🙂