Currently on version 0.2.1, and wanted to export a newly created document.

Exporting is done by opening the document, clicking Share > Download.

If I then try to import this exported .grist file, I get a warning popup which says:

Import failed: File format is not supported.

If I instead double click the .grist file to open Grist automatically with this file, I get a different error:

Error accessing document
You can try reloading the document, or using recovery mode. Recovery mode opens the document to be fully accessible to owners, and inaccessible to others. It also disables formulas. [SQLITE_CANTOPEN: unable to open database file]

Trying to enter recovery mode will show a toast message in the lower left stating

14:01:20 SQLITE_CANTOPEN: unable to open database file.

This also has a nice Report button, but when I click this I get another toast message, saying the report form isn't set up.