2010 possible head gasket

From your third picture of that gasket, I can tell its coming from the fourth cylinder hole section of it(look at the colouration differential on the right side of the gasket. Shows signs of excess heat, and discolorations when compared with other sections of the gasket).
Is that where the egr is located, seeing the excessive heat that caused the gasket discolorations at that part of the gasket?

 

On your engine block, I didn't see any signs of milky discoloration either. Probably, there's something else causing the overheating that you need to look out for.
My bet would be that the egr maybe terribly blocked, and too much temperature rises at that section of the cylinder head(that portion on the right of your third picture of the gasket), maybe what is causing the coolant to dry up(leak).
Are you getting any misfire codes, or ? I won't conclude to replace or opened up the cylinder, unless I have checked all the basic stuff first.

 

I wonder which cylinder is most prone to overheat as the egr clogs. For a 2010 with original intake manifold, I believe the EGR gas enters the intake manifold in one large diameter galley, swirls around and finds its way into any of the capillaries, one for each intake port.

When I was soaking my intake manifold with Oxi-Clean, the end nearest the EGR inlet (at piston number 4 side, transaxle end of the engine) seemed to have more carbon bubbling out, accordingly the most clogged.

There's been about four intake manifold part number revisions, and going from some pictures I've seen, I think the main revision of the newer ones is to revise the EGR passageways: to be more like a family tree: one-into-two-into-four, in an attempt to flow the egr gasses more uniformly?

Here's a must-read thread on head gasket replacement:

Blown Head gasket rebuild....@297k | PriusChat

(It morphs into complete engine rebuild.)

 

Use plastigauge to get the tolerances.