It’s very, very, unlikely this will escalate into nuclear war. Putin has already withdrawn troops from most of Russia, and will leave most of Ukraine alone as soon as he’s taken control of another chunk of the East, which seems inevitable now that his troops are focused on that.
Putin is threatening nuclear war because it is his only leverage against the rest of the world. He wants everyone to stop arming Ukraine (despite him arming our enemies in Iraq, Afghanistan, Syria, North Korea etc).
The only circumstance in which this would quickly escalate to WW3 is (1) if Putin remains in power but feels power slowly slipping from his grasp, or (2) his back is to the wall and he personally has little left to lose. He’d rather be king of ashes than not king at all. If he is either suddenly removed from power by rich Russians (quite possible) or if he remains in power but is given a face-saving option (ie the rest of world look the other way while he takes a chunk of resource-rich Eastern Ukraine), then he will let things calm down. The UN are meeting him in Moscow today, I hope about option (2).
My parents had primary school drills in case of nuclear war. Paper bags on head under table etc. It’s been a threat for a long time. Politically, things are still better now than in 1914 or 1939.
Pandemics? Yes, they happen every century or so, at least this one had an incredibly low mortality rate compared to eg bubonic plague.
As to Boris Johnson, he’s an idiot who hopefully will be replaced in the next couple of years. We’ve had poverty, riots, and bad leaders before.
The biggest issue you mention is the climate crisis, yep that is already causing mass migration from affected areas of Africa and will continue to cause more storms fires floods etc in rest of world including UK plus cause problems for crops. The migration and poverty etc will create social tensions while can lead to bad leaders emerging and wars being more likely, though hopefully not in Europe. Solving the climate crisis requires dramatic action by China and USA, the worst polluters, as well as the invention of new technologies. Anyway. It’s a long road.