I have to convert a world of the newest version on mc

I had a hardcore world that I spent hours on, I created it in 1.19.3 and stopped playing it for 5 days from the 23rd of December, on the 28th I went onto the launcher hoping to play my hardcore world when I discovered I wasn't able to open it and it required opening it on an older version of Minecraft, so I loaded a copy in 1.17 and discovered I was in creative mode in an ocean, my horse and villagers were there however, they were floating on the water, all my buildings were gone and I loaded it back on the newest version, discovering the rest of the world except the loaded bit was the same before this ordeal. I don't know what caused this but during the 5 day break I played in Infdev however I didn't load the world, all my other worlds from 1.19.3 are normal except for my hardcore one, I don't know if this is a bug or not but what do I do?