Minecraft Indev levels refuse to load

I used to play Minecraft Indev sometimes, but since the laucher got updated at June 2019, levels (worlds) refuse to load or generate, and the game crashes or go back to the title menu. (Not sure if this was a launcher bug, but this happens since they got an update).
Though Indev versions are not in the laucher, they were original versions since I got them from the archive.