Another great video from Reject Convenience, you should especially watch the part (7:29 - 10:15) about how specific location data can get with precise location on (spoiler alert: a literal battery width radius, please only allow precise location for your map app 🤢)
He also has a great tool he explains throughout the video, his privacy visualizer which you can click as you go through a site’s privacy policy to mark what they collect and how they handle the data (just collected, traded/shared, or sold?)
If you want a starting point, try looking at the permissions of the apps you have downloaded. Or try looking at Terms of Service; Didn’t Read to figure out who the biggest offenders are first and work your way up to the least creepiest providers.
The correct solution here is for courts to throw out the policies on grounds of vagueness etc. and hold the companies for the digital stalking they do. If not in the regulatory-captured US, at least somwhere else where they still give a shit about consumer rights.