The captain (boss) gets the final say. It’s important there is clarity about who is in charge. However being the boss doesn’t mean every decision is the right one. You (first officer) need a way you can convey your point of view if the decision(s) being made could have a very bad outcome. At work we follow the sociocracy workflow that has a principle of raising “critical concerns”. In aviation they say “captain, it’s imperative you listen” which is their code trigger to ensure the captain pays specific attention. Everyone needs ways to raise important questions. The boss may still choose an alternative course of action but at least both parties know how to raise their concerns.
Having a clear procedure for this type of communication may save time/money/ avoid a significant risk to you or others.