Well, there is no list of the precise differences, but the main differences ly in different parameters and additional commands. For instance, Fenix has local alpha, size_x and size_y values, div had neither. Fenix' save function requires the name of a structure/array, div wants the offset of that structure/array. if you use signal() in fenix it works directly, where in div it works at the end of a frame(when all processes have been carried out). Add to that that when you reference a non-existing process(with proc.var) Fenix bugs out of the whole program where div simply returns zero. Small things giving you a hard time with sometimes unreadable errors/performances. So to learn the language div tutorials are perfectly fine, loops, if else, program structure in processes, variables are all exactly the same in Fenix, but you need to be aware that there is no guarantee what is said in div also 100% applies in Fenix.
Consider it a yes but