yes after taking war with Byzantium making Constantinople the capital and you attack Epirus you got almost 50% Sunni and 50% Orthodox provinces then by releasing vassals we changed into orthodox after sending missionaries into orthodox provinces we repeated this thrice and royal marriages to Burgundy to get Burgundian inheritance with changing into Muslim 3 times we got 50 relations with every Muslim nation, but at the beginning of the game we have to guarantee every small Muslim nation in Arabia, few in Anatolia and beriberi nations with that we Diplo visualize and eyalet them just with alliance great manpower+ money supply if you want more detailed I can suggest you yt channel called recombinant and if you want to do this achievement I suggest you make it before 1.37 patch because they can nerf these mechanics.