Why do emojis look different on different platforms?

Unicode defines which emoji exists (the code point, e.g. U+1F600 for 😀) — but each platform draws it in its own style. Apple, Google (Noto), Microsoft (Fluent), Samsung, Meta (Facebook), X/Twemoji and others ship their own emoji fonts.

That's why a 🎉 on your iPhone looks slightly different from the same 🎉 on your friend's Android — but the meaning, name and Unicode code point are identical.