Hi, when exporting to Files, you will see a sheet appear asking you to select where to place the exported files.
If you have already added Dropbox or Google Drive to Files, then they will appear there too. They may appear at the bottom of the list and be hard to find, but there are there.
Here is a link to a video that shows them and collapsing the view: https://share.icloud.com/photos/0Uz8B4w9R_8vyMVVDHChMjcng
Does that help?