If you’re looking for help with this, sadly i would not bother.
The guidance is wrong and broken and has not been updated. The advice here is great but vague enough to be diffcult to follow, and it seems cube maps are really not a great to make high detailed sky’s anymore. It just seems clunky, over complicated and outdated.
Not sure what the solution is, but it does seem that UE likes to make these things more difficult than they need to be.