Croissant emoji is the picture of the baked pastry product, associated with French breakfast (just like the 🥞 Pancakes emoji is in relation to the USA) – it may be with or without various fillings and it is often eaten together with coffee for breakfast. So, apparently, the emoji is used in the meanings related to breakfasts and 🇫🇷 France – though it may appear in any other context related to eating, buying food, or even traveling.
Examples of using
“I love my coffee with a croissant 🥐”
“Croissants are so much better with fillings 🥐”