I saw something like this done by Jragon on Logdotzips channel, video link for reference , and was wondering if anyone had any insight on how I could do something like that.
No. Those thumbnails are very decieving. You cannot add new items with datapacks. You can only add new recipes for existing items.
I wish.. as well as new blocks.. that would be a map maker's dream.
those are retextured items i don't think that datapacks can suport nbt at the moment