https://www.minecraft.net/en-us/article/minecraft-snapshot-21w43a

21w43a states "Chunk's Level.Entities has moved to entities"

I'll fully admit I do not know in what context entity data is still found in terrain mca chunks as entity data was moved out of terrain mca files in 1.17 - However, 1.18-pre5 /entities/r.X.Z.mca chunks still use the tag name "Entities" instead of "entities" which if nothing else is inconsistent and possibly an oversight.