AFAIK
It's part of meta and the same as fb messenger, collects some data for advertising purposes. This happened about 5 years ago
The messages can't be intercepted between you and the sender, but there may be software on your actual phone that can get data from messages when you read them, or for example, your keyboard when you send messages... And that would apply on anything.
Every website collects information on people that use it. None of them care about you as an individual. Google is great example of this. Yes, Google might know that you're a gay aged 30-40 living in the UK. But they also know hundreds of other people who fit that description. If loads of them start searching for "blue flip flops" the algorithm will see that and start suggesting blue flip-flops to everyone in that demographic. WhatsApp is similarly collecting data about who is using WhatsApp not you the individual. It makes it easier for them to target advertising. It's exactly the same reason why you will see more adverts targeted at the over-70s on daytime TV than you do at night.
