Taking blame you earned is accountability. Taking blame to protect someone who lied is just covering.

Owning a mistake you made is one of the most useful things available to you, and it only works because it is true. Standing in for somebody else’s lie borrows the shape of that with none of the substance: nothing gets corrected, they learn that you absorb consequences, and everybody else now holds a wrong account of what happened. It feels like loyalty and works like concealment.

Separate the two before you speak. Say your part plainly and leave theirs for them, even when the silence afterwards is uncomfortable. If they are a friend, tell them privately that you will not be explaining it for them.