Even Vietnam wasn't formally declared as a war. Last formal declaration was WWII.
As I understand it, congress still authorized the use of force. Nowadays, the president effectively bypasses congress using the 2 decades old authorization for the use of force against the overly broad threat of "terror."
It's not a war, it's a limited engagement or whatever.
A “special operation”
A "special military operation", perhaps?
A declaration of war is an invitation for the other side to attack. Rather than being a restraint against war, empowering Congress to declare war allows them to force a potentially unwilling president into war.