The issue was resolved with additional restrictions on CSS compositing. This issue is fixed in tvOS 15, watchOS 8, iOS 15 and iPadOS 15. Visiting a maliciously crafted website may reveal a user's browsing history.
https://support.apple.com/en-us/HT212814
https://support.apple.com/en-us/HT212815
https://support.apple.com/en-us/HT212819