Thankyou for the explanation.

https://stackoverflow.com/questions/33784256/cesium-label-blurred

A workaround may be to have a perfect correlation between font textures pixels and the render buffer pixels; with this it should be possible to enable anti aliasing without causing blurring and also should reduce the artifacts when moving the camera around. This should also improve image screen space rendering as long as image and fonts are not scaled.

By rounding screen space "pixel" coordinate before transforming to normalized (0..1) screen space in BillboardCollectionVS.js shader (line 225) the rendering improves but it is not perfect:

gl_Position = czm_viewportOrthographic * vec4(positionWC.xy, -positionWC.z, 1.0);

to

gl_Position = czm_viewportOrthographic * vec4(floor(positionWC.xy+0.5), -positionWC.z, 1.0);