Newsmax occassionally experiences this issue as you described where the Live TV is not working. (not displaying the Live TV box on top). Pressing the left arrow button will bring up the side menu where you can normally select TV Live and then it will work. However, today that was not working. It will be fixed as it always is, just have to be patient.
Whenever the Newsmax Channel/app is not working, you can always watch Newsmax on the Roku Channel Live TV (channel 150). Also available on Tubi and Pluto.
The Newsmax Channel/app was working on my Roku Ultra today but not on my Insignia RokuTV earlier so was definitely device specific. It is currently working across all my devices now.
Roku Community Streaming Expert
Just another Roku user... I am not a Roku employee.
Insignia RokuTV, Ultra 4660x, Premiere+ 3921, Express 4k+ 3941