At the bottom of the main Steam Featured page is a list section with some tabs. One of those is "Upcoming". If you click on that, then click on the "Upcoming releases" button at the bottom, even when there are Linux games showing in that list in that tab before clicking it, the page it takes you to with the filters along the right side is always blank for Linux. If you change the selection to Mac, that is blank as well. But, if you change it to Windows, suddenly you get all the upcoming games results including the Linux and Mac games.