A cookie management issue was addressed with improved state management. This issue is fixed in Safari 18.1, visionOS 2.1, tvOS 18.1, iOS 18.1 and iPadOS 18.1, watchOS 11.1. Cookies belonging to one origin may be sent to another origin.
https://support.apple.com/en-us/121571
https://support.apple.com/en-us/121569
https://support.apple.com/en-us/121566