Financial institutions decide if they support Quicken and, if they do, which versions. If they have opted to support on Quicken for Windows then you won't be be able to import that into Quicken for Mac. I would suggest reaching out to the institution and asking, specifically, if they support Quicken for Mac. If not, tell them that as a customer this is a feature you'd like to see for your account.
In response to your problem, there is a workaround, if you're comfortable modifying the QFX file.You can open the QFX file with a text editor, and you will see that it has a series of tags, such as this: <Tag>Look for: <FID>{some text}</FI><INTU.BID>{some text}or:<FID>{some text}</FI><INTU.BID>{some text}and replace the {some text} with 10898:<FID>10898</FI><INTU.BID>10898Save the file with the .qfx extension. You should be able to import it now. Quicken may ask you to link accounts found in the QFX file with those you may already have in Quicken.10898 is a valid Financial Institution (FI) code (Chase Bank).
I had the exact same issue but different brokerage. I have tried every thing I could think of as well as pouring over this site and others. I even accused them of turning the feature off! Finally I stumbled on this and presto. . . SUCCESS. It's inexplicable because I use Chrome! Go figure. https://www.quicken.com/support/message-when-using-online-services-its-not-your-fault I'm definitely ready for a beer after all this!
I have the exact same issue. Quicken 2017 for Mac. TransAmerica 403b that I can't download. Quicken needs to step up and work with institutions to get this FIXED!