@g12
RTE feature is provided by default for the RTE enabled form fields and provides a basic set of features provided as default at [0] so don't think there is emoji support in RTE with AEM Forms OOTB.
However with AEM core components, RTE functionalities are made available via a series of plug-ins, each with features property. There is a blog to enable emoji here[1] with core components.
[0]: /libs/fd/af/runtime/clientlibs/widgets/richTextField/javascript/GuideRichTextField.js
[1] -
http://experience-aem.blogspot.com/2020/05/aem-6540-core-components-280-touch-ui-rte-rich-text-edito...