"According to Chapter VII of the United Nations Charter, only the UN Security Council has a mandate by the international community to apply sanctions (Article 41) that must be complied with by all UN member states (Article 2,2)."

https://en.wikipedia.org/wiki/International_sanctions

For the US, congress is supposed to approve of wars but that has not always happened either.

"It has been alleged that the War Powers Resolution has been violated in the past – for example, by George W. Bush invading Iraq in 2003 or by President Bill Clinton in 1999, during NATO bombing of Yugoslavia."

https://en.wikipedia.org/wiki/War_Powers_Resolution

Thanks.

Allowing the UN to enact sanctions (or conduct armed warfare) does not prohibit or preclude UN member states from doing so on their own.

Given that the UN's main job is supposedly to maintain peace, one would hope so.