Two things-“apostolos” means to send for - like an ambassador or messenger-so in one sense all Christians are apostles and those ordained bishops spiritual descendants of the original apostles.Jesus’ friends, disciples, his first apostles where Jesus’ “unique” messengers" for one time and one place in history.Just as we are 'sons and daughters " of God but Jesus was the “unique” one and only Son of God.
It is a very nice thought to think that all Christians are apostles but is it really true? I certainly understand the Pope as an apostle through Apostolic succession and of course, I can see Bishops as apostles by virtue of their succession/laying on of hands at their ordination. In fact I can see where all Priests and Deacons by virtue (again through laying on of hands) of their ordination are apostles since they have all been “sent” with a mission to spread the gospel. However, here is where it gets a little tricky. It’s here where we have to ask the question “What is a Christian”.
If you mean a person baptized in the name of the Father, Son, and the Holy Spirit, one confirmed by the One, Holy, Catholic and Apostolic Church, then I can certainly see that since they are confirmed by successors of the apostles and are “sent” with the mission of bearing witness to Christ.” (Catechism of the Catholic Church, paragraph 1313) then I can certainly see that.
Outside of that it’s difficult to say definitively who is clearly an apostle of Christ.
I’m not sure that a person who says they believe in God and has asked Christ into their hearts but has not been baptized in the name of the Father, Son, and the Holy Spirit is an apostle because it does not appear to be historically consistent.
However, I’m not going to say that this (unbaptized/unconfirmed) person did not receive personal revelation whereby the Holy Spirit named them as an apostle and “sent” them on a mission.
What we do know is that baptized Catholics confirmed through apostolic succession are “sent” with the mission of bearing witness to Christ and at each Mass are “sent” to be Christ present in the world.