If they are considering it they should mark this highly-voted idea as under consideration:
https://community.esri.com/t5/arcgis-experience-builder-ideas/allow-arcade-expressions-in-experience...
2022 they have not added Arcade to the roadmap and have indicated no plans to support Arcade e.g.
https://community.esri.com/t5/arcgis-experience-builder-blog/experience-builder-2022-roadmap-and-bey...
2024 it's still not in the roadmap but a comment from @Jianxia "support for Arcade expression at the framework level of Experience Builder is under the consideration. So you can use it for dynamic text or filtering. However, this is the capability beyond 2024 due to WAB parity. Thanks for letting us know."
https://community.esri.com/t5/arcgis-experience-builder-blog/arcgis-experience-builder-2024-roadmap/...
So it appears you are limited to using it in the Web Map, and they may focus on it later after they've replaced Web AppBuilder completely.
