"IOS 15.3 will prevent Safari data leaks."
The first security flaw was detected earlier this month. Apple then hastily unveiled a new updated version. The latest version does not feature any new features, only the security bug in the Safari browser. And so to be safe you must use the version.
Although the latest versions of iOS and iPadOS have been released, there is still a security flaw in the Safari browser for devices running the Mac operating system. And so you need to use the Safari browser with caution on devices running the Mac operating system.
Source: The Verge