approaching vs upcoming

approaching is a noun but upcoming is not a noun.

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

As adjectives, approaching and upcoming are synonyms defined as:

Other synonyms of approaching include coming, forthcoming.

approaching (noun)	upcoming (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

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