After the ArcGIS Online October 2023 update, Administrators are no longer able to add a user to multiple groups.

Solución alternativa

For an Administrator, assign members to multiple groups using this workflow: https://doc.arcgis.com/en/arcgis-online/administer/manage-groups.htm#ESRI_SECTION1_76A1DDC1944548DC84CD4ABBEDF21C2F.

Pasos para reproducir