Hi.
To extract from barrels, the player left clicks on the barrel.
While in creative mode, this breaks the barrel, leaving none of the contents.
I think it'd be a good idea to have left-clicking in creative mode still extract from the barrel.
Maybe left-clicking while sneaking would break it?

Sure! If I can figure out how to do it, I'll add this feature in.

I'm actually going to hold off until Fabric provides a config mechanism (which by the looks of things seems like is on the horizon?) since sneak-left-clicking conflicts with extracting an entire stack. Not quite next release, but soon you'll be able to choose which behavior you want!