Targonian aspects are celestials, whose powers have entered mortal hosts. Such as Atreus, into whose body the celestial aspect of war has entered. Meanwhile the ascended (Shuriman) are just former mortal humans who have been ascended by the power of the sun disc, a magical artifact. The Targonian ascended basically have actual gods in them while Shurimans just have the power of the sun disc.
"Are Aspects and ascended celestial avatars in 2 different region?" is a weird question. The Shuriman ascended roam in Shurima, there aren't that many left to begin with. Nasus, Renekton and Azir have a reason for remaining. Former Shuriman ascended, the Darkin, on the other hand roam across Runeterra after being imprisoned in their weapons after the Darkin wars.
The Targonian ascended (the guys with gods in them) hail from all across runeterra, like Taric is a Demacian, while Atreus actually comes from one of the Targonian tribes. They just go where they are needed and aren't bound to the mountain in a sense that they cannot roam far from it. Hopefully this helped you a bit.