Esri recently released ArcGIS Enterprise 12.1, but we are still waiting for a compatible version of ArcGIS Experience Builder (ExB).
According to the ExB release compatibility matrix, the most recent Experience Builder Developer Edition version supported by ArcGIS Enterprise 12.0 is based on ExB 1.18, while newer Developer Edition releases are available. I attempted to develop a custom widget using React 19 and Experience Builder Developer Edition 1.19, then deploy it to an ArcGIS Enterprise 12.0 portal. However, I encountered compatibility issues during deployment.
Based on Esri's blog announcement, Experience Builder 1.21 was expected to be released in May 2026. Until a compatible version becomes available for ArcGIS Enterprise 12.1, we are unable to take advantage of React 19 and other enhancements provided by the newer Experience Builder releases when developing custom widgets for deployment to Portal for ArcGIS 12.1.
