If we port high quality video games made for PC to mobile platform, how much will be tge difference in graphics

I was trying to create my first ue5 high graphics game build for PC and maybe potentially for consoles as well. And I know that its apparently easy to port games in UE. My question since always is, how much will the graphics reduce when you try to port a very high graphic/texture PC game to mobile platform? The textures I used are either 4k/2k & nanite, majorly.

So if I port a game which was meant for PC and is very graphics intensive overall, will UE automatically reduce the LOD or the quality of the textures so that it can run on a mobile platforms weak chipset?

How does porting a graphic intensive game from PC to mobile work?