Apologies if this is a duplicate. I used the search function and found no issues related.
Anyways, let's begin.
So some updates ago, tools break after passing 1 durability, instead of 0. This makes sense as before it made little sense for tools and armour have 0 durability.
However, mobs can still drop items that have 0 durability, when the minimum is 1.
Duplicate of MC-136374. No worries for not finding it