MNDAA are descendents of ethnic Han Chinese who ran away to Burma to escape from Manchurian Qing dynasty forces which took over ethnic Han dynasty Ming. MNDAA itself was a faction of the second iteration of Burmese Communist Party formed by China after the original BCP collapsed. They are armed by China, and as seen here, takes directions from Beijing.
NUG formed by democratically elected parliamentarians from 2020 election is seen by Beijing as being too close to Western governments and thus is not favored by China. EAOs under the influence of China including the largest militia in the world United Wa State Army do not cooperate with NUG.