DANGER!!! DANGER!! DANGER!!
I applied this update to a Pro, and it went fine.
I then tried the regular 4K (the $19.88 one). It is bricked. It gets stuck at the Google TV animated logo. I tried a factory reset, and it complains some files are missing. Unless there is a way to force a deeper reset via the USB port, it is probably trash.
And I am not the only one:
https://www.avsforum.com/threads/walmart-onn-4k-streaming-box.3198184/page-45?post_id=64030288#post-64030288