Was having issues with apps using full screen and mirroring. Spent time on the phone with Verizon and Samsung. No real progress at all. Finally discovered the problem is DEX. DEX doesn't allow mirroring. It worked, but when I reset the tablet, it didn't. The same app I used originally would not mirror after the reset. Got a message that "smart view is not available in DEX". Totally bizarre. If the app doesn't have the maximize button, full screen won't work in DEX. Netflix would allow full screen in DEX if I opened the Netflix app and then tablet settings (gear icon). Only after I started a movie or program. Didn't have to change anything. Netflix would go into picture in picture and give the full screen option. Xfinity stream didn't allow that. Also, Xfinity won't allow mirroring. They block it. Go Comcast! There is a program "DEX Max" that will put the maximize button in most app windows, but some will not allow that. Netflix and Xfinity are such apps. Some bank apps won't either. They detect the apk has been modified and won't allow bank access.
Full screen and mirroring work in tablet mode.