So one of the things that western sanctions actually achieved was hampering certain military technologies that Russia used to import. The most infamous of these were semiconductors but there were many more; cnc machines, high quality ball bearings,image processing and analytical components, fcs systems fir tanks, optics/thermals for all armor, transistors, DC converters etc.
Initially Russia was buying these critical western made pieces from 3rd parties, effectively bypassing the sanctions, but it was still not enough to make up for the shortfall of the high quality western versions. This is why Russia deployed its old soviet stockpiles; it had to play catch-up, while trying to source an ever increasing demand for these products.
Now it looks like western sanctions have backfired and Russia is able to produce what it needs domestically, while relying on China as a guaranteed trading partner:
Officials said that Russia uses machine tool shipments from China to bolster its production of ballistic missiles, and that Chinese microelectronics are used in the production of Russian missiles, tanks, and aircraft. The officials said that 90% of Russia's microelectronics imports in 2023 came from China.
Chinese businesses such as iRay Technology and the North China Research Institute of Electro-Optics also supply Russia with military optics for tanks and armored vehicles, they said.
Along with these supplies, Chinese businesses may also be furnishing Russia with nitrocellulose, used to make propellants for weapons. The officials also told reporters that U.S. intelligence indicates that China is illegally providing satellite imagery to Russia for use in Ukraine.
Our view is that one of the most game-changing moves available to us at this time to support Ukraine is to persuade the PRC (People's Republic of China) to stop illegally helping Russia reconstitute its military industrial base," one official said.
Chinese Foreign Ministry spokesperson Mao Ning responded to Western criticism in a press conference on April 10, saying the partnership between Beijing and Moscow constituted normal cooperation. "China will not accept the accusations and pressuring," Mao said.
https://www.reuters.com/world/us-says-china-is-boosting-russias-war-machine-ukraine-2024-04-12/Some content in relation to this.