iCloud photos can not be moved from main library

We users here in this forum cannot answer for Apple's opinions and plans other than what they have announced. As far as we can tell, what you are describing is a basic part of the library design in Photos as shared by iCloud, iOS, iPadOS, and macOS. Albums are merely lists of photos in the library; any given photo can be in multiple albums or none at all.

Are you asking about Photos for Mac or Photos on the iPhone or iPad?

In Photos for Mac you can still use the "Hide" feature to do what you want with the help of Smart albums but this is not possible on the iPhone or iPad.

Previously we could simply hide a photo in the library but keep it visible in the albums. It is no longer possible to do this on the iPhone or iPad however, as Apple has changed the hiding tool from a tool to temporarily weed out the library to a tool to keep certain photos secret as many users requested. So we lost the ability to hide photos temporarily from the library, but keep them visible in the albums. Hidden photos are now hidden everywhere and we even have to unlock the Hidden album to see them.