When a list is filtered you are only seeing the rows that match the filter. The other rows are still there, just hidden. If you want to make the same entry in a group of filtered cells you can’t use the fill handle to drag and copy as you will overwrite the hidden rows. There is an easy way to do it.
Excel has a keyboard technique that allows you to make the same entry in multiple cells and this works perfectly with filtered lists.
The shortcut is Ctrl + Enter – hold down the Ctrl key and press Enter.
In the filtered list select the range you want to enter into and type the entry but don’t press Enter. Hold the Ctrl key down and then press Enter. Then release the Ctrl key.
This leaves the hidden rows untouched.
Here’s a short video showing the technique.