Nether Data is broken

So, My friend has a realm, 1.16.1, that I and a couple of others play on. There are a whole bunch of problems with Realms, and one of the people that wants to join gets kicked every couple of minutes. We tried troubleshooting literally everything we could think of, so I offered my server up. I set it up to allow my friend’s ip’s through, then swapped my world folder with his, but our nether was entirely reset. you spawn above a pit of lava, and we had a decent amount of portals and stuff. Any help would be very much appreciated!

well… im guessing you only replaced your overworld with your friends world folder

so your world_nether and world_the_end folders are still the same. In the world folder, copy the contents of DIM 1 and DIM -1 to the world_nether and world_the_end folders respectively. (Make sure to have backups)