There has been much confusion around bundles experimental feature: (see MC-256518)

While it is working as intended as far as the playerbase that use bundles seems concerned, the description on the datapacks, coupled with the blog post about feature toggles ( https://www.minecraft.net/en-us/article/testing-new-minecraft-features/feature-toggles-java-edition ) makes it appear they would suffer the same limitations as other experiemental features (e.g. unable to upgrade worlds using them).

There doesn't appear to have been any official communication from Mojang that bundles remain a "special case" as we transition to the feature toggle system, and that the feature toggle is purely for a recipe and creative tab entry.

The description for the bundle datapack should indicate this, and other official comms. should explain that it's still "available" even when not selected, due to it being the last? WIP item left over from C&C.