So, I haven't been entirely successful in moving MSFS 2020 sceneries into MSFS 2024 which has prompted a few questions:

1. Can it be done, and--is it as simple as moving the sceneries from the old Community folder into the new Community folder?

Here is the location of my MSFS 2024 Community folder; 

C:\Users\Owner\AppData\Roaming\Microsoft Flight Simulator 2024\Packages\Community

I tried moving Kahului which is four separate sceneries into my new Community folder, but it doesn't indicate any change on the MS map (for creating flights) and when I go to the airport (PHOG) the scenery clearly isn't there.

Yes, copying to the community folder, or even using the 2024 Addons linker to point it to the community folder should work in most cases. I tested some 2020 addon airports and some work with no issues, some have some minor issues and one that simply does not show up in 2024, similar to your experience. I have no idea why it does not show up in 2024, but I can't really complain as it is freeware released way back for 2020.