loading into a 1.16.4 world on 1.18.1 completly destroys the world

I was playing on a different world on 1.18.1 and i wanted to play on another world that was made in 1.16.4. I loaded into the 1.16.4 world with 1.18.1 forgeting what version i was in and without any warning of upgrading the world. I noticed my texture packs werent working so i check to see why. I then noticed they werent working as i loaded into the 1.16.4 with 1.18. I load out of it and go back to 1.16.4. I tried to load into the world but was given a warning message that it could break the world. I create a backup after id converted the world to 1.18 and load into the world using a copy of the world. This created a big block of grass over where i was before and deletes any that was once there. I check the world properties after making another replica of the orignial world and saw the world made 64 blocks of air. Is that the end of that world now? i was playing in optifine but i believe that has no effect on the issue. I know this isnt exacly a bug i didnt know how else to communicate my problem to anyone thanks.