I know that Troy posted about the blank rectangles that should be app.
I’ve tried his suggested workaround ie launching from launch manager.
It worked for a while in as much the icon was there but empty, then it just disappeared again.
I get the same thing with Sincler, there’s another blank there also can’t seem to determine what that one is.
I also have a 4K everything is listed and working fine on that, regret buying the 4K Max.
I have a max and don’t have any missing icons but it depends on the app developer and if he coded the app for the new Fire OS. What I did was switch to the Wolf Launcher and the launcher manager. All my icons show in there. If some still don’t show then at least you can give the Icon a name in the modification settings.