When I am going to save the 512x512 sticker icon in photoshop. It shows the 215 KB size of an image which is more than 100 KB. I want the 512x512px size png icon in 100 KB. How is it possible?
I suggest you use
Save for Web under export.
You should see a window pop up like this
This will offer you more options to strip back content you don't need. I regularly use this to cut down web banner animations I have made in After Effects to GIF files less the 150kb. It will also give you a preview and estimated file size so you can see play around with the settings and see what works best for you without exporting lots fo files.
If you are still struggling to reduce the image I would suggest looking at simplifying the artwork, such as less colour, rasterise/reduce amount of effects applied and just removing anything that isn't needed.
Once you have saved the sticker icon in png, go to an image compressing website (my current favorite is optimizilla.com), upload your file there and it will reduce its size.
If you use optimizilla, you can select how much you want the size to reduce. But do remember, image size is reduced by compression which also lowers the image quality, so dont reduce it too much.