Nvidia is a great example of why a flat rule like this wouldn't work. Nvidia pretty much just does one, pretty specialized thing (GPUs) and trying to break it up into >10 pieces worth <$20B each (approximate median GDP of African nations by IMF) would be completely unnecessary. Just their gaming GPUs had ~$6B in profit in just the last year alone, and we know that their market cap comes much more from the AI market. We definitely could use stronger anti-monopoly laws, but market cap limits aren't the way to do it.