[PeterisP]

As the adtech data sharing usually doesn't fall under any other legal reasons that would allow you to use that data, you need to get consent for the new companies. If the user ignores your email and takes no action (doesn't opt in), you don't have their consent, and can't share their data with the new companies.

But IMHO that's the whole point, the legislation is a response to users saying that they don't really want such companies to exist - the business practice of taking my private data and sharing it to the world 500 companies will now require my explicit opt-in freely given consent (i.e no "we'll refuse service if you don't consent"). The expectation and intent of this law is that I and pretty much every one else will simply not provide that consent, and that business practice will become impractical and die out, as it should.