Import, process images, then Export, using a single hard drive

This works fine, a lot of people work with a computer with just one volume.

Import: You can import from any compatible external or internal volume. If you insert a camera card to import, you’re importing from an external volume. But if you already copied the pictures from the card to a folder on your computer and removed the card, you can also import from that folder on the one volume in your computer. Lightroom Classic lets you choose whether you want to import by leaving the photos where they are, or moving/copying them to another folder.

Edit: Photos are edited from the folder they were directed to in the Import dialog box. If that folder is on your one volume, of course that’s OK.

Export: You can choose to export to any folder you want. Many people choose an export folder on the one volume in their computer.