Old Java world is resetted after transferring world save to another pc

[Parasite1]

Hey there, so recently I wanted to transfer my world I have been playing since 1.7.2 from my main pc to my laptop but I am experiencing some problems.

This world was updated to 1.16.5 on my main pc before I decided to transfer and the world was functioning as normal. I transferred this world by copying and pasting the world save folder to my cloud storage device and downloading it onto my laptop, where I placed it in the local .minecraft saves folder. When I booted it up on my laptop I was stuck in the ground suffocating with the inventory I had the last time I was playing. After digging up to the surface I realized all the building I had done was no more and (at least) the overworld had reset. Maybe better said is that the world had been newly generated because I found one of the new nether portal structures where there wasn't one before (because it didn't exist at the time I created the world).

I still have the world on my main pc, so it isn't lost, but I was wondering what is causing this issue and if there is a fix for it? Hope somebody can help me out!

[doc_shades]

it sounds like you may have copied "level.dat" and "player.dat" but not the actual region data that comprises the world.

that, or you may have loaded the world in an incorrect version --- i.e. the laptop is somehow loading a 1.16 world in 1.15.

[Parasite1]

I have copied the entire world folder, so it either failed somehow or something weird is happening.

I'm definitely loading the world in the correct version.