Repair Minecraft World. 1.16.5?

I and a couple of friends built a world that was on 1.8.9, now after a long time wanting to switch to 1.16.5, we also did by changing the version at Athernos (the server just runs over it). Nothing else, but now there are the new buildings etc. Not only the mobs… But can I somehow change that so that all our buildings etc. Are there + 1.16.5 without having to rebuild it? If I just reload the seed on the 1.16.5, the built auvh is not there, right? Are there possibilities or can you copy the buildings out for Worldedit or something

If you have a backup from the old world, you can import it again. Probably your old world was overwritten with the version change and everything is gone without a backup.