what is the optimal size on splash and icon image as my look distorted?
For Icon, you can use 512x512px Image.
For Splash: https://websitetoapk.com/forums/401-size-resolution-custom-splash-screen
It is recommended to use 720x1280px or 1280x1920px.
This icon pattern is due to latest material design guidelines, as you can also see on many other apps. The icon fits between the circle to make it look similar to all others. But one thing that you can do to get some large icon is that you should make your edges rounded and transparent as the outer circle holds inner image with small margin. You simply need to know that if you use rounded icon it will show the biggest possible, you can try out with that.