What is this symbol called? A blue rectangle with a red dot
The symbols with the red dots are schottky diodes, as Bimpelrekkie stated in comments.
The red dot indicates the unused pin.  This device comes in a SOT23-3 package, which has 3 pins, of which only two are used.  I don't know why they used a 3-pin model in ADS for this, since you don't do pcb layout in ADS, and don't care about that 3rd pin for RF simulation.
Well, no one I know uses ADS for PCB layout (and I work in an RF design group).