Modern Africa wouldn’t have the U.S. or Europe supplying it so it would have to rely upon its own industrial base, designs, and expertise and would be starting from scratch on producing ammo, replacement parts, jet fuel, etc. It would have an initial tech advantage, but 1939 Europe would have British and German scientists and engineers working to reverse-engineer captured modern tech and the Soviets simplifying the designs for mass production. The African countries also lack strong military traditions and recent experience fighting other standing armies (Egypt is the only one with old experience fighting Israel) and in conducting maneuver warfare. 1939 Europe would still have WWI and the Spanish Civil War in its living memory and would have some of the best military minds of the modern era at its disposal (Guderian, Zhukov, Slim, Kesselring, Franco, etc.). 1939 Europe wins and it’s not a close call.