For healthy people, a colonoscopy would only be offered after a positive stool test:
Cochrane compared the stool test with sigmoidoscopy:
Comparison Of Two Methods Used In Screening For Colorectal Cancer, Cochrane, October 2013
Mortality from colorectal cancer was reduced with FOBT [fecal occult blood test] screening and screening with flexible sigmoidoscopy. When we compared the two methods, we could not conclude that one was better than the other.
The US Preventive Services Task Force says that among all the screening options (stool tests, sigmoidoscopy, colonoscopy):
There are no empirical data to suggest that any of the strategies provide a greater net benefit.
And that once you’ve reached 75, if you’re in good health you can probably stop screening:
In adults ages 76 to 85 years, the age at which the balance of benefits and harms of colorectal cancer screening becomes less favorable and screening should be stopped varies based on a patient’s health status (e.g., life expectancy, comorbid conditions) and prior screening status. Limited evidence suggests harms from colonoscopy, such as perforation and bleeding. Modeling studies estimate that generally, few additional life-years are gained when screening is extended past age 75 years among average-risk adults who have previously received adequate screening.
In adults age 86 years and older, competing causes of mortality preclude a mortality benefit that would outweigh the harms.
Here’s an example of an at-home colon cancer screening test (this is not an endorsement): Cologuard