Is Polygon PoS still considered a sidechain?

Hi!

Few time ago, there was some confusion about it but Polygon PoS was defined as a sidechain, not a Layer 2.

1/ Today, is Polygon PoS still considered a sidechain (vs a Layer 2)

2/ Nowadays, there are plenty of Layers 2 but most of them are still very centralized. So what makes them different from Polygon PoS (if it's still considered a sidechain)?

Thanks!