Very good.
If you read 1 corinthians in one shot. It explains itself. I want you to keep in mind there is no "chapters" in scripture. its important because the section that follows tells us more.
If I were to presume the teaching total depravity no doubt we can fish for things can presume Natural Man to mean an unsaved individual. That equation was not made.
That is not what it means at all. we all have a natural man.
Lets start at the start.
1 Corinthians 1
2To the church of God which is at Corinth, to those who have been sanctified in Christ Jesus, saints by calling, with all who in every place call on the name of our Lord Jesus Christ, their
Lord and ours:
His audience are saved people who are being saved. But there is trouble in that church.
1 Corinthians 1
11For I have been informed concerning you, my brethren, by Chloe’s
people, that there are quarrels among you.
1 Corinthians 1
18For the word of the cross is foolishness to those who are perishing, but to us who are being saved it is the power of God.
1 Corinthians 1
22For indeed Jews ask for signs and Greeks search for wisdom;
23but we preach Christ crucified, to Jews a stumbling block and to Gentiles foolishness,
24but to those who are the called, both Jews and Greeks, Christ the power of God and the wisdom of God.
25Because the foolishness of God is wiser than men, and the weakness of God is stronger than men.
26For consider your calling, brethren, that there were not many wise according to the flesh, not many mighty, not many noble;
The whole according to the Flesh = natural man. That points out to our common secular understanding.
Heres the part that follows let me put it together with your citation. Remember theres no actual chapters the whole thing is together.
1 corinthians 2
14But a natural man does not accept the things of the Spirit of God, for they are foolishness to him; and he cannot understand them, because they are spiritually appraised.
15But he who is spiritual appraises all things, yet he himself is appraised by no one.
16For WHO HAS KNOWN THE MIND OF THE LORD, THAT HE WILL INSTRUCT HIM? But we have the mind of Christ.
1 corinthians 3
1And I, brethren, could not speak to you as to spiritual men, but as to men of flesh, as to infants in Christ.
2I gave you milk to drink, not solid food; for you were not yet able
to receive it. Indeed, even now you are not yet able,
3for you are still fleshly. For since there is jealousy and strife among you, are you not fleshly, and are you not walking like mere men?
4For when one says, “I am of Paul,” and another, “I am of Apollos,” are you not
mere men?
So here we have Paul explaining to people he declared "those who have been sanctified in Christ Jesus, saints by calling," as not ready for the the things of the spirit. They are infants in Christ. And that even the reader is not ready. "for you are still fleshly" ( i will underline this above)
This might open another can of worms because some folks understanding is a person is instantly regenerated and thus receiving gnostic understanding of all things. But here he is talking to those sanctified in Christ "natural man"
Everyone is still "FLESHY" "CARNAL" "NATURAL MAN".
The subject doesn't change from chapter 1 to 3. These Christians in the process of being saved are the "Natural Men"
This is a matter of someone starting with a philosophy and just fishing for their own meaning of a word without actually just trying to determine what exactly Paul is SAYING.
I understand how a person indoctrinated with philosophy wants to see:
14But the UNSAVED MAN receiveth not Jesus or The Gospel of GOD: for they are foolishness unto him: neither can he know IT, because they are spiritually discerned.
But if you just read what it SAYS and follow it into the next chapter. You are going to see he is clearly talking to CHRISTIAN BELIEVERS. Who just haven't reached that level of maturity. ( example: they had guys having affairs with their step mothers)
14But the natural man receiveth not the things of the Spirit of God: for they are foolishness unto him: neither can he know
them, because they are spiritually discerned.
15But he that is spiritual judgeth all things, yet he himself is judged of no man.
16For who hath known the mind of the Lord, that he may instruct him? But we have the mind of Christ.
(the next "page")
1And I, brethren, could not speak unto you as unto spiritual, but as unto carnal,
even as unto babes in Christ.
2I have fed you with milk, and not with meat: for hitherto ye were not able
to bear it, neither yet now are ye able.
3For ye are yet carnal: for whereas
there is among you envying, and strife, and divisions, are ye not carnal, and walk as men?
4For while one saith, I am of Paul; and another, I
am of Apollos; are ye not carnal?
Paul is still having to talk to them as a "natural man" They are not going to get it yet.
Hope this helps.
PS. I picked up this explanation from a youtuber you can prob do search 1 Corinthians 2 Kevin Thompson