This means that users running iOS 18.3 or earlier versions of the operating system will only see a blank icon if someone running iOS 18.4 or later sends them a message with the new emoji.
you have to design an icon that still looks like a redwood tree, or whatever you're interested in, even at extremely small size, because we use emoji in text. And that's where a lot of proposals ...
In the second iOS 18.4 beta that Apple released today, there are a selection of new emoji characters, including bags under eyes, fingerprint, leafless tree, root vegetable, harp, shovel ...