Emojis sometimes split.

Entering emojis may or may not divide (decompose into two characters).

I think it depends on the web service and application I use, but how does it break up?

I just happened to try Sublimte Text and found that the editor had one character emoji as shown in the attached image, but the title (file name?) part was divided into two characters.

I would like to know the reason why it is simply divided.

I'm also asking because I want to get rid of the vague fear that something might go wrong when using string determination (e.g., simple string determination (if statement) or regular expression) or saving it to the database.