I used Evernote for over ten years, long before the cloud features came along, and left when nodes couldn't have multiple parents in the outline.
At that point I had several dozen GB in forty notebooks, and had to MANUALLY copy and paste to get my data out.
The file format is proprietary, no OPML or any other open-standard format export target.
They do this, as in turn IBM, Microsoft and Apple have done/still do, to "lock you in".
Last time I make that mistake.
Workflowy while less bells & whistles, allows for plain text-based OPML bulk export of the outline tree.