You're right, the transfer of arms between warring and non-warring countries is something of a nuanced problem. On the Iranian side we're talking about cheap drones that Russia could do without, while on the US side the US has sent literally the equivalent of the entire Russian military budget to Ukraine twice. The only reason Ukraine is still standing is because of the USA. This is not true for Russia and Iran. But, there is a case to be made by Ukraine that they might want to launch a war with Iran and DPRK to stop their weapon supplies. When Ukraine decides that, they can prosecute that war.

On the North Korean troops, we still have zero confirmation on them being in Ukraine at all. Only yellow journalism from Ukraine and the West. I will wait till I see proof before I believe it. But again, even if Korea was involved, Ukraine could declare war on DPRK and fight then to stop their support of Russia. Let me know when they decide to do that.

Who is escalating here? The USA. Russia, in 1992, made clear and transparent what they could and could not defend against militarily. They sought a security framework that would mutually maintain the security of Russia, the former Soviet republics, and Western Europe. They even sought to join NATO to achieve this. One of the things Russia stated it could not defend against was a nuclear capability and a ready military presence in Ukraine. To maintain security in the region it was mutually agreed that Ukraine would remain neutral and that NATO would not expand Eastward.

In 1992, after the meeting that established this, Bill Clinton immediately went to his generals and asked for a plan to get Ukraine into NATO. Immediately. Duplicitously. Every expansion of NATO nuclear capabilities and military readiness Eastward was an escalatory step.

Russia, at every turn, warned of the threat but appeased and appeased and appeased because they wanted to be integrated into the world economy and they had established their escalatory red lines. The escalations through the 90s and early oughts were below their red lines.

Then, the escalation got worse. The coup in Ukraine in 2014, where John McCain and Victoria Nuland were on the ground celebrating, was a clear escalation along a security red line and for that Russia responded by annexing Crimea.

The escalation from the West continues as Ukraine began killing ethnic Russians in the Donbass and Ukraine and the political elite of the US got closer. The escalation got to the point where Russia had credible intelligence of military readiness being deployed at the Ukraine border and political discussions of admitting Ukraine into NATO.

Again, Russia chose not to appease this escalation and launched an SMO to create a limited invasion to achieve several goals: 1) protect ethnic Russians in the Donbass, 2) engage Ukraine in a border dispute so it couldn't join NATO, and 3) militarize the border to establish readiness in the face of increasing escalation.

Russia was immediately willing to negotiate with Ukraine but the US and UK made it clear that Ukraine was not allowed to negotiate on its own behalf. Instead they essentially delivered more materiel than Russia's entire military budget for 2 years. Each delivery was an escalation of more and more lethal technologies, but was also coupled with intelligence, special forces, and other actions, each of which were escalations.

Russia has responded to each escalation. But Russia itself has clear goals that it has stated from the outset and has been willing to negotiate on for literal years. And they are the same goals they stated in 1992 while negotiating with the lying duplicitous Americans.

As for whether Russia is the only one threatening nukes, I think you'll find that the USA unilaterally withdrew from multiple nuclear treaties, has openly stated they were building a nuclear kill chain in the Pacific to counter China, openly discussed winning a nuclear exchange, openly discussed developing tactical nuclear weapons, and is the only nuclear power to have ever used nukes against targets. Those targets were primarily civilians, by the way.

So, you can continue to pretend that history started when you want it to, you can pretend that Ukraine and USA are passive victims with no agency who have never done anything that could be considered escalation, and you can pretend that the USA deploying nuclear-armed submarines to Korea and nuclear-armed b52s to West Asia are not threats of nuclear war, but if you do, there's just no reason to engage with you because you're not participating in reality.