Lumen is the lighting system. Nanite is the technology allowing you to use much (like, orders of magnitude) higher polygon counts in a scene (basically an infinitely dynamic LOD*). You can download the early access UE5 now and I've got to say, they are lightyears ahead of Unity, technologically.
Considering how beginner friendly UE is (visual scripting, graph based material editor, etc.), and their (IMO) much better pricing scheme**, I think UE will eventually replace Unity as the go-to engine for indie devs unless Godot really step up their game.
* This is an oversimplification. I don't really know what I'm talking about
** completely free until $1M in revenue, then 5% royalty. You also get free access to Quixel Megascans and Mixer (which are normally quite expensive) and full access to the source code. Not to mention MetaHumans which is a game-changer in itself
Considering how beginner friendly UE is (visual scripting, graph based material editor, etc.), and their (IMO) much better pricing scheme**, I think UE will eventually replace Unity as the go-to engine for indie devs unless Godot really step up their game.
* This is an oversimplification. I don't really know what I'm talking about
** completely free until $1M in revenue, then 5% royalty. You also get free access to Quixel Megascans and Mixer (which are normally quite expensive) and full access to the source code. Not to mention MetaHumans which is a game-changer in itself