Apple has released the first betas of iOS 18.3 and macOS 15.3 to users, but unfortunately, these versions do not include the redesigned Mail app that was introduced in iOS 18.2. The new Mail app features a modern look with smart categorization, but it is currently only available on iPhone devices. Marketing images suggest that the update may eventually reach iPad and Mac devices, but no release date has been confirmed. This isn’t the first time Apple has rolled out updates differently between devices, and some users have criticized the new Mail app feature. However, iOS 18.3, iPadOS 18.3, and macOS 15.3 are expected to be released to the public sometime between January and February.
Source: https://9to5mac.com/2024/12/16/new-mail-app-ipados-macos