Emoji are standardized by Unicode, but Unicode does not force Apple, Google, Microsoft, Samsung or other platforms to use identical artwork. It defines the character, name and technical data; each platform designs its own image.
That is why 😊 Smiling face with smiling eyes or ❤️ Red heart may look slightly different depending on the phone, app, browser or operating system. The meaning is usually shared, but the style, color, angle and expression can vary.
Differences matter most when an emoji has a subtle facial expression. A smile that looks friendly on one platform may look flatter or more awkward on another, especially with emojis such as 🙂 Slightly smiling face.
This is also why newer emoji may appear as empty boxes or missing symbols on older systems. The platform needs font and artwork support before it can display the emoji properly.