I have the same model but I have the 49". I've been having that same problem for the past 16 hours. I've tried everything from all of the different post and YouTube videos. I left it on resetting itself every few seconds, and when it finally stayed on for a few minutes I went to the settings. What I finally tried is putting it in retail mode and now it's working perfectly. Now I'm trying this same trick with my 2018 65" NU7100, hopefully it'll work a second time
The issue is surely with the software update, it has nothing to do with the hardware. The Smart Hub (not smart at all) always updates the software whenever the TV is turned on, even there is no new update. Due to some bugs within the software, the update could not proceed, so the TV keeps turning on and off.
I solved the problem by renaming the TV <EDIT>
I purchased the TV from Costco, and I will have it returned, I believe it will eventually go back <EDIT>