Whoever may change a list’s or a canvas’s access now also chooses who can share it. People who can edit is where every list and canvas starts, so nothing changes until somebody chooses. Under Anyone with access, a person who can only view it can share it too, at Can view, and never changes or takes away anybody’s share; a guest who can only view never shares. Each change is in the audit log.
A list or canvas in a public channel is read by the whole workspace and edited by the channel’s members, its owner and managers, and the people given Can edit. The Share dialogs say so.