Yes, you can! Just go up to settings, click "Room Details" and scroll down to "Permissions" and toggle "Add Content."
When enabled, people entering your room will be allowed to add content like stickers, gifs, YouTube videos, games, drawings, and more. While turned off, people entering your room will be restricted to a view-only mode where they can't add these objects. However, members will still be allowed to move, alter, and delete existing objects in a room. To prevent this, you can lock all the objects in a room under the "Manage Content" section in settings.