Steps to Reproduce:

Create a Hardcore mode world.

1. Create a same seed Creative mode world.
2. Find the Minecraft Preview data storage folder.
3. Navigate path: com.mojang/minecraftWorlds.
4. find Hardcore mode world folder’s level.dat (and level.dat_old) files and move they to Creative mode world folder (Remember delete Creative mode world’s level.dat And level.dat_old files)

Observed Results:

it is Hardcore mode but it allowed me to fly and not take damage and it created an infinite items/blocks.

Excepted Results:

it should be a Hardcore mode world but that’s glitched. Even I haven’t Administrator Privilege but I still can fly and not take damage. Also I can get infinite items/blocks.

Summary:

moving level.dat file from Hardcore world to Creative world and it is Hardcore but it allowed player to fly and not take damage and it created an infinite items/blocks.