32 bit vs 16 bit art design

There's a bit of ambiguity here: 8 bits per channel (+ alpha channel) is often referred to as 32 bit - which is not at all the same as 32 bits per channel.

For painting, 16 bits per channel should be the standard. With 8 bit data, you only have 256 discrete steps per channel, which will lead to visible banding.

You may still see banding on screen with 16 bit data, because your display pipeline is still 8 bit (unless you have a 10 bit capable monitor) - but in that case it will only be an on-screen artifact, not in the file itself..

It would be 16 or 8 BPC for standard dynamic range images that are not truly High Dynamic Range (HDR), which requires 32 BPC to contain the extended lighting/exposure information. 32 BPC mode is restricted to certain tools, which would tend to cramp "artistic" painting and edits.

https://helpx.adobe.com/au/photoshop/using/high-dynamic-range-images.html

https://helpx.adobe.com/au/camera-raw/using/hdr-output.html