think of the CG (Center of Gravity) as the point that an aircraft will balance on a pin (single dot)
ideally the CG and the Reference Datum they speak of on that doc page should be relatively close
but they are not the same, the CG moves with loading, and its certainly possible to load aircraft to not be balanced (think of a canoe, the cg will move way forward if you load a second person, and a third may sink you :P)
thats what your looking at in that tab
not all aircraft can keep the allowed weight balance in the green with all load outs that may be possible (making it that way might severely restrict what an aircraft can do), this is a normal limitation of design, if you want say a twin otter that can carry more weight in the cargo area you may not be able to just carry 2 pilots with no cargo and stay in the green- its up to the pilot to load the aircraft so it stays balanced enough to control
Datum reference for good measure (the pics show where the modeller places the “Datum”, we ‘try’ to get it fairly close to what the CG will be)
https://docs.flightsimulator.com/html/mergedProjects/How_To_Make_An_Aircraft/Contents/Modelling/Airframe/File_Setup.htm