upcoming vs approaching

upcoming is not a noun while approaching is a noun.

Word	Noun	Adjective	Verb	Adverb
upcoming	No	Yes	No	No
approaching	Yes	Yes	No	No

As adjectives, upcoming and approaching are synonyms defined as:

Other synonyms of upcoming include coming, forthcoming.

upcoming (noun)	approaching (noun)
	the act of drawing spatially closer to something
	the temporal property of becoming nearer in time
	the event of one object coming closer to another

upcoming (adjective)	approaching (adjective)
of the relatively near future	of the relatively near future