Is it possible to zoom in further than the scale of 1:70 on a default ArcGIS Online basemap?

No, it is not possible to zoom in further than the scale of 1:70 on a default ArcGIS Online basemap. This is because it is a set limitation of the basemaps in ArcGIS Online.

In ArcGIS Online Map Viewer, a basemap determines the scale to which the users can zoom in or out. The default basemaps in ArcGIS Online contain 23 scale levels ranging from 1:591657527 to 1:70 and users cannot zoom in or out beyond those values.

However, it is possible to zoom in further than the mentioned scale by creating custom basemaps or getting high resolution imagery. There are also no limits on zooming if a dynamic map service is added. To set a custom scale range, users must publish their own basemap service either to ArcGIS for Server or to ArcGIS Online as a tile map service. This service can be used as a background basemap layer that allows users to zoom in further than the maximum scale.