How do people monitor an investor’s portfolio? Isn’t that private?

This is an example that Michael Burry exited all their investment positions. Just curious isn’t this private information to share? Or does investor like warren buffet and others request to choose to share in purpose? Such disclosures help maintain market transparency and can influence others’ decisions. Sometimes, investors might time these filings strategically to send signals or manage market reactions. Ultimately, it’s a mix of legal obligation and strategic choice.?!!