ModernGL is a python module for accessing OpenGL. While Blender already has an api for this (bgl) it does not support certain features required for conversion to mesh. (Compute shaders, which are available in 4.0+ under the gpu api)

Similar reason as above. The rendering engine uses bgl/openGL. Which has been deprecated in later versions of Blender.

support for 4.0 and newer versions is planned.

Because the Conjure Vision rendering engine is written in bgl, Blender's openGL api. Which Mac doesn't support anymore.

Updating Conjure to support 4.0+ should also enable support for MacOS.

SDF stands for Signed Distance Field. It is a mathematical representation of shapes with unlimited detail. They also allow for very accurate and performant boolean operations. There are no polygons at all (until you convert the SDF to a mesh of course)

Not at all, it sits alongside other workflows such as SubD. You should combine techniques when and where they work best. Conjure is great for primitive shapes with large smooth blends between them. (Ma.K aka Maschinen Krieger comes to mind)