For a comprehensive list of other examples of issues with item positions in the Creative inventory, click here.
All tickets associated with item placement in the Creative inventory are valid for cases introduced in 1.16 and later as per this comment. Exceptions exist, which are valid for their own reasons.
Ancient debris is an ore (according to the following blog post: https://www.minecraft.net/en-us/article/minecraft-snapshot-20w06a) - as such, it being grouped with other ores in the Creative inventory would be expected. This, however, does not happen.
- Open the Creative inventory
- Locate Ancient Debris in Building Blocks
- Locate Gold Ore in Building Blocks
- Locate Iron Ore in Building Blocks
- Note that there is a considerable distance between these items