The DOJ and SSA regularly prosecute social security fraud.
Take a look at the website of the Social Security Administration's Inspector General site and look through the news releases.
However it's likely not as common as Musk wants you to think.
That's fine, but far from showing a serious focused fully staffed fraud detection operation.
Of course, such an operation may exist, but I haven't seen any evidence.
The top SS fraud case in that list is a couple of idiots who basically reported themselves: https://oig.ssa.gov/news-releases/2025-01-30-husband-wife-se...