[fandangos]

If my TV natively supports 120Hz and it's a 4k TV, what should I whitelist?

I have yet to test this on Kodi 19 but you should not have to whitelist anything.

If you whitelist 1080p your tv will do upscale since Kodi will output in 1080p. For 1080p content.

Kodi will use the highest resolution you have, change to 23.976 for movies in that resolution.
And AI upscaling will be enabled for any sources.

Just leave it be.

Ok, so I won't whitelist anything, just like in my 18.9 kodi. Seems to work fine without touching it.
But isn't the Shield doing upscaling as well?

One test I would like to try is to stream DV content like Soul from Syncler and play it in your Kodi build and see how it works.

Last question, is there a way to export all my settings, add-ons and everything I did in 18.9 to the build you created?

Shield will upscale if you set it to do it. 
You can see the settings pressing the menu button and looking at AI upscaling. 

In Kodi libraries are not interchargeable between versions. 
But when you set everything up, just use Kodi Backup addon, back it up and restore. 

Just beware and pay attention to what version of the addon you're using. I wasn't able to restore a backup a had because of versions missmatch. 
I believe for Matrix it's version 1.64. So use that and when restoring use this same version.