This downloads the stems currently visible in your project, using whatever version is selected for each stem. For example, if your vocal stem is set to a restored version and your bass stem is set to the original version, the export will include those current versions.
To change what gets exported, first select the version you want on each stem waveform, then click Export again.
If you need to create stems first, use the Universal AI Stem Splitter or open the project in Studio.