I was breaking wool on a survival world with unenchanted shears and accidentally swapped super fast between my Eff 5 netherite axe and the shears and it insta-mined the wool.

I tested it out in a creative world with no datapacks, no mods, completely vanilla 1.21 AND 1.21.1 and the behavior is still there. It's not just shears that it works with, I was able to insta-mine calcite, almost could with stone and tuff, all with an UNENCHANTED WOODEN PICKAXE. Same goes for dirt and grass with a wood shovel, etc.

Guide to Recreate:

• have both an efficiency 5 enchanted tool and an unenchanted tool that is effective on the block you are going to mine in your hotbar.
• as you start mining, swap between the tools by hitting the number keys on the keyboard super fast.
• Profit for some reason?????

My guess is that in swapping between tools, the breaking script is running BEFORE the script that re-updates what enchantments your tool has, thus 'copying' them to the new tool. Seems to only happen with efficiency or any speed enchantment, but not with things like silk touch, fire aspect, etc.