An apology with a “but” is an argument dressed up in a nicer outfit.

Everything before the but gets deleted by everything after it, and the other person hears only the second half. What arrives is a case for why you were justified, delivered in the tone of an apology, which is more irritating than a plain disagreement. The urge is understandable, because you probably did have a reason. The reason is a separate conversation from the repair.

Say the sorry and then stop talking. Let the silence be uncomfortable rather than filling it with context. If your side genuinely needs saying, raise it another day, once the apology has landed by itself.