I'm upgrading 10.2.5 to 100.7, in 10.2.5 one of the ways i've used animations is: when selecting entity on map, i've created a circle around it which grew and shrank with wpf transformations, this made it easy for the user to see which element is selected on map, is there a way to create same behavior in 100.7?
Not at the symbol level no. You'd have to do it on top (or frequently update the properties of a symbol to create the illusion of animation). Also see Control Template in 100.x runtime sdk