Standardize an extension to the Set-Cookie header for a "Purpose" field. This field if unset means the cookie is essential (local laws now still apply so if a website misrepresents a non-essential cookie as essential then that's illegal just the same way as implementing a fake cookie banner or not implementing one (if you need it) is illegal). Now in my browser I can set my cookie preferences to only store and send essential cookies.
For other tracking methods that don't use cookies there's already DNT and all that's needed is for a local law update to clarify what it means and to enforce its use.
These things would actually make sense as opposed to the current situation where the EU makes it sound like cookies are something a website forcibly stores on your computer and uses.