[LongMan]

I forgot about the index file. It contains the identifying info for a folder of nodes. Take for example, the sub menu nodes that i suggested that you copy and modify. the folder for movies contains an index file with label, 342, which I suspect is movies in English and get translated to the equivalent word or expression in other languages. When you copy for your 4K movies you might want to change that label. The truth I only find that index file useful when browsing nested nodes ie a folder within a folder.

One question I had, and I'm not sure if this is due to Kodi or (again), my misunderstanding: I copied all of my /userdata/library files from one machine to another, but on the other machine when I go to the new nodes I created, they just take me to the files options, like Movies, TV Shows, 4K Movies, 4K TV Shows as opposed to the direct view I expected.

Remember I pointed out that the setup you see in Estuary has three separate pieces.
Main Node (Given Above) btw this is the titles nodes in the default set
Nodes for Widgets (necessary modifications given Above)
and a folder of nodes that you that you see labeled Categories for the top row. (copy the default and modify)

You need a Main Node 4K Movies, the nodes for the widgets, and a copy of the default nodes modified with your rule for the Categories widget.

I am not sure that it is worth the effort for the categories. Maybe just point to the defaults. I find I use the main and widgets most of the time