Am I right in thinking you can not save a progressive jpeg from the "export as" dialogue? I can't see it there, but I can't understand why Adobe would make such a fundamental feature unavailable. Am I missing something?
Use Export - Save for Web (Legacy) - all the options are there
This is a really long work around when you have exported multiple Artboards and you want them to be progressive jpgs... You will have to re-open each jpg one by one to save as progressive. They should just add the option to the Export As function.
I've been having to export artboards as jpgs, then doing a batch save for web (legacy) to save as progressive. Like Edward said, it's a long workaround.