"Supposed" is the past participle of "suppose". "Supposedly" is an adverb usually used to modify a whole sentence. (EX) That Japanese guy is supposed to be a linguistic racist because he always says "What is your nationality?" (EX) Supposedly that Japanese guy is a linguistic racist because he always says "What is your nationality?"
so basically there's no difference between this two words [suppose to be and supposedly]? its just that they're being use in a sentence for modification, right?