Can someone please explain to me how the collection of contact data is in any way legal under the GDPR and why Microsoft (Windows), Apple/Google haven't been required to make changes to prevent abuse of this permission (such as selecting specific contacts).
I'd also like to not know why if my contact data is shared, I am not informed of this. If my data is uploaded by Google to their servers, I should know. If somebody chooses to share my data with $app I should know, and, be able to "opt-out" of being included, perhaps (although it should be opt-in!)
Being able to mass collect what is often the most sensitive information means that consistent data is now a liability; keeping the same number/email can be useful for cross-referencing. Ideally you should rotate what data you can (physical address/location is obviously extremely difficult). Everything else is possible (browsers/IP addresses/emails/User Agent strings, phone numbers etc etc)
The best idea is to "troll" with your data; put insane items in your logged in basket (ebay/amazon etc), like sex toys. You can even make an order (and refund it) to further poison the well. Log in to Google and do some disgusting searches, and train algorithms to have the "wrong idea" about you, this is a reality we're now facing as this data can (and will) be used against you at any opportunity.