Can you provide some information re: which basemap / dataset you are referring to? Also - as a couple of quick checks - are you doing this via ArcGIS Pro or ArcMap, and how is your internet connection?
Thank you for your response. I tried to load imagery data online, it couldn't. I did it using Arc GIS Pro 2.7, but this I did in Arc GIS 10.8 can be done or the data can be loaded. I have a stable internet connection with a speed of 15Mbps. Please more advise about this.
An alternative approach to using the insert Basemap button is to connect to the REST service through Catalog. This will get you most of the standard Esri Basemaps:
Catalog > Servers > Insert new ArcGIS Server Connection
URL = https://services.arcgisonline.com/arcgis/rest/services
Then drag and drop the service onto your map.