Xbox One/Series S/SeriesX and PS4/5 are x86 PCs, Switch is an ARM phone.
So, in the lowest level they are pretty out of the shelf hardware. Electronics are getting way to complicated to invest in the development of custom hardware architectures for a single product.
You take a commonly used architecture, fork an Operating System that you have access to, bundle as many libraries as makes sense and call it a day. No one is going to use weird quirks of the hardware except if you make some deal with Unity or Unreal.