https://en.wikipedia.org/wiki/Wikipedia:Reliable_sources/Perennial_sources
You can notice a bias towards the state media from pro-capitalist regimes from the above.
Might I recommend King Leopold's Ghost if you want a straight up history book of the Belgian Congo. No shade against Heart of Darkness, I think that's a worthwhile read; but reading KLG first will give you more context to appreciate HoD. Or maybe read it after, idk, up to you