World of almost 3 years was reset to a brand new world

This is the third time logging in my world on the 1.17.0 update l. Everything was fine untill i went into the nether, when i loaded in it was completely reset and had new terrain. When i went back through the portal it spawned me in a random location and when i got back to my home coordinates nothing was there. I didn't even realise i was in the same location because it had updated terrane. The only things that weren't reset were the stuff in my inventory. So i guess make a copy of your world before you play the new update r.i.p my 3 year world and im afraid to load my last save of the world in case it happens again.