You can create an "air pocket" that looks like a real air pocket but can still drown you.
How to reproduce:
- Create a body of water that is at least 4 blocks deep
- Go into survival if you weren't already in that gamemode
- Type in /give @s bucket 9
- Select the buckets and spam right-click until you see an air pocket
The air pocket is not really air, so you can't use it to your advantage.