I too am experiencing the Launcher Hijack issue on the 2019 Fire HD 10 I just got. It worked flawlessly on my HD 8, but on this one it sometimes does what others have said here - goes back to the default launcher for about 5 seconds, and then goes to the Nova one - and other times (most of the time, in fact) it just goes to the default one and flat out never switches to Nova, as if Launcher Hijack wasn't even on the device. I'll definitely be following this thread to see if/when this issue gets a fix. In the meantime, I at least uncluttered the default screen as much as I could by putting all the default apps I don't use into one folder. Still can't move the icons to the bottom of the screen and leave an empty space above as I like to do (for the sake of better wallpaper visibility), but it'll have to do for now.