Can I import Windows 8.1 Minecraft worlds to Windows 10?
Solution 1:
The operating system doesn't have anything to do with the format of the worlds. It depends on the version of the game you are transferring from and transferring to.
create a backup before using the feature I'm about to explain.
A feature called "optimize world" was added in Minecraft 1.13 and it can convert older worlds to the new format. I'm not sure which versions are supported by this feature though. To optimize a world, go into the singleplayer menu, select a world, click edit and click optimize world.