Minecraft: built things are no longer there?

I just registered with version 1.14.4 (optifine) in my world (?) and before that I played with 1.15 all the time because I just wanted to see what was changed. I then went back into the world (1.14.4) and all of the things I built were gone. The world also looks like I deleted the world and re-entered the seed of the world (hopefully you know what I mean). The funny thing is that everything is still in my inventory, e.g. Elytra, armor, etc. I really want to have my old world back but I really don't know what to do.

Yes, if you don't have a backup, it doesn't look good…

There's always a warning about the worlds, right?

Why do you press xd anyway?

The world has been reformatted into a different version and a lot seems to have been lost.

Why do you press xd anyway?

Everyone does. Even I don't make any backups, despite 200GB + free SSD storage.

A 1.15 world doesn't work in 1.14 either. The world was re-created and overwritten. Inventories are stored differently, which is why you still have them when there were no 1.15 items in them. You can't get to your old world without backup.

Oh.

Unfortunately I did not make a backup: / oh man… Well, thank you anyway.

Bad

Unfortunately, that's true.