Did the process changed since it was first published in 2022?
https://www.esri.com/arcgis-blog/products/arcgis-enterprise/developers/add-experience-builder-custom-widgets-in-arcgis-enterprise/
Also, at the end of that post there are two good questions and it will be helpful, if there was a response to them.
1. When you say to install experience builder, does that need to be on the machine that hosts the enterprise?
2. Is it possible to add custom widgets to ArcGIS Online too?
@Jianxia