You can export multiple artboards using the Export Persona. Not only can you export multiple artboards, but you can do so in multiple file formats, with a different format for each artboard, if desired. You also have detailed control over the export format.
Simply show the Toolbar via View > Show Toolbar or press ⌥⌘T and then click on the Export Persona button.
Another interesting feature is Continuous Export, which is best explained by this video:
I think Affinity Designer has the best export feature set available. I am not affiliated with Affinity in any way, but I'm happy to answer any questions.
