What a strange way to think about a telecommunications service. By the same logic, shouldn’t there be a privacy policy for regular old phone lines? Who knows which third parties are between you and the person on the other end!
And speaking about the other end: I have bad news about all the data you share with untrustworthy contacts on WhatsApp…
Quite practically, anyone that enables backups (which WhatsApp heavily nudges people to do) uploads a copy of all your messages and media sent to them to a cloud provider you have no privacy agreement with.
old telephone lines did not disclose info about me with merely my phone number. whataspp discloses name, picture, status
As for your second comment, updated first comment with:
I am not even sure how this is GDPR-compliant if that app is European. They do not have my permission to have my private data, and GDPR does not allow whatAspp to hand it over without my permission either...