call back ads companies to get your ad id/cookie, so also don't:
- cross-reference which posts resulted with viewing the articles and ads in those articles
- cross-reference which posts resulted with viewing which products in stores
- check with ads companies which "competition" you switched to and with what content you interacted there
- have info on how your demographics' profile (things you interact with) connect with the content you watch
  - so also, they don't sell this data back to ads companies
process which content you interact with in order to make you stay on the platform longer or trigger you to write angry comments so you create content for others
process at what local times you view content in order to process how to target your demographics
process what you chose to not interact at all (only view, no vote)

I'm afraid I could go on but I think you get my point

Someone could be scraping how you vote, what you write, how you write, at what times you write, etc. But for outside scraper there is no way to make sure (from that info) which ads you've seen on article sites and what things you bought or browsed. So yes, open-source, federated, socially-run platforms are better for your privacy