world corrupted after 1.16.5 release

I see the same issues reported. In my case all villagers gone, all golems gone, all bred animals gone, copper and amethyst no longer exist. I see them marked as resolved but I see no resolution. I understand you have created two incompatible versions (which I would love an explanation for as well) but just a statement the two are incompatible is not a resolution.

How do we get back to the other launcher? My world is wrecked and a backup does no good since I have no way to revert to the previous release.