By default only 1,000 will display in the Data Source Pane Window. Your data is still there in its entirety. You can change that value if you'd like, manually entering a new value. Hope that helps! Thx, Don
Once you import the data then in data source, It will show you 1000 row only like below image
But Actually It imports all data from data source. Once you bring the data into the sheet to create graph then you can see all data.
Please mark correct and helpful if it works for you.
Just circling back to see if your question was answered? If yes, please mark this response as correct to close the thread. Thanks, Don