For nuclear attack on another country you would be right.
For an invading army inside borders is would be a scenario like this: there would be a very clear warning to leave or we will nukes at that hour the same day as the border was crossed. A warning goes out for citizens to evacuate. The missile silos are visibly readied to show you’re serious. Warning goes out to other countries that this is an internal matter and not aimed at anyone else. Then you fire If the invaders haven’t left. There would not be a second attempt at invading.
It’s what people assumed when Putin said last year that Russian nuclear doctrine allowed two possible thresholds for using nuclear weapons: retaliation against a first nuclear strike by an enemy, and if “the very existence of Russia as a state comes under threat even if conventional weapons are used”.
That’s how you strongman. Instead Russia is in denial for a week and then comes with “maybe we should do something?”