need to know more about the Web pixel or app pixel

[1080]

why the shopify has given the web pixel - or app pixel name sandbox ?

1. it is still beta versions ?
2. why we want to move the assest or theme app block to the app pxiel ?
3. app pixel is loading into the iframe so it can access the main root document ?
4. for Pixel and ga4 type app can be work fine ?

5. for if any store has using the custom or third part app for the "add to cart" feature still the add_to_cart happend in pixel ?