Since 1.19.3 it is no longer possible possible to create custom worlds by importing JSON files, as the "Import Settings" (and equivalent export option) buttons have been removed from the world creation UI. This was caused due to the creation UI redesign.
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However, this issue is Working as Intended.
The report you have submitted is working as intended: see the 23w05a changelog:
Please note, that mechanics of the game may change between updates.
Things such as graphics, sounds, world creation, biomes, redstone, villagers, and animals may not work the same in current versions.
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