AES?

"Actually Existing Socialism". It's a term that emphasises that a state project is currently socialist rather than some hypothetical (usually) western idealised socialism. So when people in, say, the UK are criticising Cuba or China or some other state it is worth bearing in mind that they are doing so from within a capitalist and imperialist system and what they are criticising is a socialist movement and should be analysed with that in mind.

But can't Russia or China veto UN Security Council resolutions?

Russian Federation was very much, before the SMO in Ukraine in 2022, entangled with following the western line on international issues. Similarly, China's reform and opening up and ascdency to the World Trade Organization (WTO) in 2001 had relinquished its foreign policy lines to nonintervention and liberalism (it also felt threatened by the DPRK nuclear buildup).

The imperialists believed that the fall of the USSR would strangle all other socialist nations. In Korea, when the north experienced a famine due to weather catastrophes, the US waited to see if this would induce regime change. Millions of famine related deaths later, it did not.

Today, the DPRK enjoys the mutual military and economic cooperation with Russia and China has also had a steady friendship with Korea, allowing remittance workers to settle in the border between the two countries for labor and travel opportunities (there's also special economic zones with Russia) Russia is not enforcing the embargo and neither will China when it comes to those instances.

This doesn't mean the sanctions and embargo on Korea do not still harm it. But that the DPRK can navigate around these challenges and find solutions to come out the other end.

Also the image of the DPRK during kim jong Ill's period from 1990s to 2011 is one where the imperialist stereotype and dehumanization campaign against the north was at its earnest (as NK was named in bushes "axis of evil" speech). Your views are a product of that period.