YubiKeys are vulnerable to cloning attacks thanks to newly discovered side channel

Seems like a "blast door" type problem...

That sounds like the attacker would need to basically already know how to unlock it...

It's like saying a bank is vulnerable if you have enough drills and guns

On the contrary. China for example is known for accessing traveler electronics both during customs/immigration checks and in their hotels. Unless the victim carries their key on their person at all times without fault it can be cloned without them knowing.

i have physical access to my own yubikey and can't make a backup copy. someone else who only temporarily has access to it being able to do so is definitely a vulnerability.