This is the Western opinion based on the shits like 38North, Rand, Washington institute, etc...all based on South Korean secret services, if not outright defectors. In fact western fantasies.
My source is a reliable person, that knows very well NK. As U can see, NK's industry is capable to produce its own ICBM, SLBM, in a very near future its own nuclear propulsion submarine, locomotives, and its thermal electric powers, etc..... As U can guess, all these assets imply strong tool machinery and high-skill personnel. Seeing this, it is normal to see NK's next step is the development of aero engines, thus aircraft industries.
Things are more complicated than it would seem. Aircraft is in essence an offensive weapon, not a
defensive weapon. Russia and China do have strong relations with Japan, and South Korea, if they help NK to have offensive weapons, it does mean they want to cut relations with South Korea, Japan, in fact, the rest of Asia. USSR could in its time, because soviet leaders did not have good, or tight relations with the West. As U can see it is not the case with Beijing and Moscow leaders.
Hence neither China nor Russia can afford to help NK, on contrary, they applied the embargo against NK. Moreover, they agreed with the West to vote on several resolutions against NK in the UN assembly.
The myth of Russia or China did help NK is mere fake news spread by western intelligence agencies. Most of NK's technologies were developed by north Koreans.