Minecraft → World with extended height deactivated?

For some time now I have not been able to open two of my worlds because it says "The loading of the worlds with extended height is deactivated". Does any of you know how I can change that? The version with which I opened the worlds is 21w17a, so, as I said, I can no longer open them. I'm really looking forward to any helpful answer (and maybe an explanation, if you can change it). If more information is required, just write!

Try an older snapshot version