To work in disconnected mode, webmaps can be configured offline in Fieldmaps. To take webmaps offline, all the layers of the webmaps must be enabled for offline use.

To enable offline feature layer on ArcGIS Online, refer to: https://doc.arcgis.com/en/arcgis-online/manage-data/take-maps-offline.htm#ESRI_SECTION1_C0331D55CAE14D4FAB1B54354A9246F2

To enable offline feature layer on the portal for ArcGIS Enterprise Server, refer to: https://enterprise.arcgis.com/en/portal/10.9.1/use/take-maps-offline.htm