@hallvors @mmasnick @FantasticalEconomics you could also just pick a number?
The Digital Services Act for e.g. “classifies platforms or search engines that have more than 45 million users per month in the EU as very large online platforms (VLOPs) or very large online search engines (VLOSEs).” Perhaps the figure (obvs wd be lower for USA / UK laws) could be different depending if the platform offers Portability and Interoperability with other platforms.