There is one reason, and only one reason I disagree with the article you've linked here. It says "Putin has no option left except a nuke" and this is true, but it overlooks one thing. When Russia tested Nuclear-capable missiles early in the war, they were shot down. Their Kinzal has proven unable to evade Patriot interceptors. Their nuclear-capable bombers have proven easy-prey for anti-aircraft systems.

In other words, I have no doubt Russia has made up their mind to use nuclear force, but I don't think they have the means to actually deliver it anymore.