When using adaptive icon packs they go by system. You can't change the shape and have all the icons uniformly as circles. The shape I prefer. Having it as a system setting will insure that the icon packs when applied can be changed to circles effectively.
It is built into Android 16 on Pixel phones, it should also be on Samsung phones for those that don't want to use ThemePark.
The first screenshot is the icon pack in a folder that makes them circles. The 2nd screenshot is the icon pack applied by the system shape.
