If you are T-Mobile subscriber, T-Mobile will automatically on April 26, 2021 start sharing your online and device usage data with advertisers unless you opt-out of such sharing (see link). While this clearly would not be permitted in the EU, it is permissible in the US.
If you don't want T-Mobile to share your data, open the T-Mobile app on your phone, select the “More” option, select “Advertising & Analytics”, and then turn off “Use my data to make ads more relevant to me”.
But, before you think that T-Mobile is the only communication provider doing this, AT&T similarly allows for the use of its customers' web browsing activity for ad targeting (see AT&T Privacy Policy at the section "Choices about how we use...").
Photo by Mika Baumeister on Unsplash