On the topic of the Ukraine war spilling into global nuclear war, this was slightly reassuring. It's the opinion of "former British army officer and former commander of the UK & NATO Chemical, Biological, Radiological and Nuclear (CBRN) Forces":
www.cnn.com

Opinion: The most likely nuclear scenario | CNN
How worried should we be about Putin's finger on the so-called nuclear button? In this Q&A, former British army officer and nuclear expert, Hamish de Bretton-Gordon, unpacks the military jargon and argues all-out nuclear war probably isn't on the cards anytime soon.
The use of strategic nuclear weapons is extremely unlikely in my opinion. This is a war nobody can win, and at the moment it does not seem likely that this regional conflict in Europe would lead to a global nuclear war which could destroy the planet for many generations.
I am sure the checks and balances are in place in the Kremlin, as they are at the White House and 10 Downing Street to make sure we are not plunged into global nuclear conflict on a whim.
I believe Putin’s tactical nuclear weapons are unusable. Even if their vehicles do work, the minute they turn their engines on to move they will be picked up by US and NATO intelligence.
I hope the private discussions the Biden and Putin administrations have apparently been having are along the lines of, ‘you move your tactical nukes and NATO will take them out with long range precision guided missiles’. It would appear this is the case from what Jake Sullivan, the US National Security Advisor to the White House, disclosed over the weekend.
The most likely nuclear scenario is, I believe, an attack by Russia on a nuclear power station in Ukraine. This could have a similar effect to a tactical nuclear explosion but would be easier to deny for the Russians, who accuse Ukraine of deliberately bombing their own power stations.