Hey there! I’ve worked on native emoji support, so I can help clarify.
The UI Builder uses the Editor Font Fallback chain which has emoji fallback setup. At runtime, you are using a different TextSettings than the editor one which explains the differences. You’ll need to setup your own TextSettings for your runtime UI Documents. For Emoji support, you’ll need to assign your own Color Emoji Font in the TextSettings fallback. This process is briefly explained in the documentation.
Keep in mind a limitation: Some OpenType font features, such as chain context and single substitution, aren’t supported.
I noticed you’re using color modifiers, which TextCore doesn’t fully support due to its lack of OpenType support. However, we’re working on a new TextGenerator that properly supports these features. If you’re interested, you can check it out in this thread. Note that it’s still behind an experimental flag in U6.
Hope this helps! Let me know if you have more questions.