Hi @Joe_TV_ ,
If you use UTF8 code in subject line box, it will consider it as a string and in inbox it displays as it is the entire UTF8 code provided in the subject line.
To add emoji in subject line you can try two ways,
Either the 1st way is, copy the emoji 🛠️ and paste it in subject line

or 2nd way is to create your Emoji in 'Emoticon list' which you can directly call in subject line.

To create Emoji in this dropdown, go to Administration > Platform > Enumerations and click the Emoticon list and follow the steps mentioned in this document - Click here