Moved into new (to us, built in 1980) house 2 years ago. Installed an Airthings radon meter a year ago. Levels get up to 400 Bq/m3 when all the windows are closed. Finally had a radon mitigation system installed. Will hopefully get to much safer level below 100 Bq/m3.
A little radon gets produced by basically all rock on Earth, but some types (like granite) emit more than others (like limestone). In the US, it’s a bigger concern in the midwest and mountain areas than the south or parts of the west coast. You can look up EPA maps to show the areas of relative concern.
Worldwide, though… I had trouble finding much detail.