quote: the new blueprint for beginning wartime in the 21st century.
No, and inappropriate.
First, your critical infrastructure should not connect to the public internet, so should be safe.
Second, an invasion is not a war/fight, it is a rape. The rules of war/pugilism do not apply. There are no restrictions in self-defence.
The appropriate response to an invasion from day 1 is to use insurgents to abduct and vanish the invader's MPs, senior military, key regime members, and the wealthy who enable the regime.
Targeted strikes on their internet/telco backbone will end their membership of the modern world.
Still not surrendered and left your turf after a month or two of damage? Well, you gave them a chance to mend their ways. Time now to target their crown jewels. For any fossil fuel rich nation, that would be their energy resources. Small bombs, big bangs. The pipes, the wells, the fields, the nukes. You would be able to see your invader's country burning from Mars.
That should do it. Someone invades your country, it shouldn't be a 'war', it should be the end of their regime. 3 years? It shouldn't last more than 3 months.
The battlefield stuff and the cyber stuff is just a brutal, unethical sideshow. The people who organise wars and invasions should be the people that suffer and pay for them, rapidly and directly. Not civilians and conscripts. Ordinary citizens dying for the sins of their political leaders - that is a crime against humanity.
History warns us to never invade someone else's country. Ethics aside, there is no benefit in it. It always ends badly and leads to decades of toxicity. Just don't do it. If you want to take a country down, just covertly leverage schemes like Brexit and Project 2025 in those countries. They will take themselves down whilst you sit back, eat popcorn and watch.