There's no need to break down a stack of cloud berries into single items for taming.
Just throw the entire stack at them and wait. They will eat from it when they are hungry, so it doesn't matter if it's a stack or a single item.

But more to your advantage, throwing a stack at them also means you won't get up more often, thus less chance to startle them in the first place.

From the wiki:

Notes
Creatures only eat one item from stacks so the food doesn't have to be thrown one by one. Player base structures can be used to prevent the food from despawning.

https://valheim.fandom.com/wiki/Taming

Thorin :)