The key word of Isaiah 7:14 is "sign". Understanding that word will clarify the sign itself.
Therefore the Lord himself shall give you a sign; Behold, a virgin shall conceive, and bear a son, and shall call his name Immanuel. Isa 7:14
David was a man after God's own heart [1 Ki 15:3, Act 13:22]. In contrast is this king Ahaz to whom Isaiah is speaking. Isaiah offers him a sign from God, but Ahaz, while feigning piety, rejects it. So, Ahaz rejects Isaiah and now has rejected God. God, however, says He will nonetheless provide a sign.
With that in mind, the question arises what kind of sign from God will this sign be? Some doubt God that a virgin will conceive. Some instead feel that the sign would simply be a young woman getting pregnant in the normal way. But obviously, a normal conception in the normal way can hardly be taken as a sign from Almighty God.
Matthew and countless future Christians understand this. A sign is a miracle, a token, a mark, a signal, a beacon. A sign is not something normal.
So yes, Isaiah 7:14 is a prophecy of Immanuel; that is, God with us who is Christ Jesus.