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.
Fans must be placed outside because a leak after the fan can be bad. Now in all honesty, that only holds true if you have bends and twists and turns. I personally think you can place it in a basement or attic as long as you have a straight continuous pipe going up.
As bonus you get passive suction when the pipe is warm.