That’s actually a rather standard teaching. Per Paul, we sleep until the second coming… then we are resurrected and live in peace on the new earth with Jesus as lord.
Paul also said:
“For to me to live is Christ, and to die is gain. 22 If it is to be life in the flesh, that means fruitful labor for me. Yet which I shall choose I cannot tell. 23 I am hard pressed between the two. My desire is to depart and be with Christ,
for that is far better” (Phil 1:21-22)
He believed that dying was better than living because the dead person would ‘‘be with Christ.’’ If he actually believed that humans are unconscious until the end of time, I find it hard to see why he would call that better. So I don’t think it’s accurate to say Paul believed no one is in heaven yet.
Humans require both physical bodies and souls otherwise we would not be humans. Jesus is human and so he ascended and (catholic teaching) we also have the Assumption of Mary. If the soul was enough why would they need to be both body and soul in heaven?
Human beings are not complete without both their body and soul, but that doesn’t mean the soul can’t live without the body.
Believing that Jesus is only spirit is a gnostic teaching that none of the mainline christian churches teach.
True. But I don’t see what that has to do with whether or not souls are in heaven right now.
In both the Nicene Creed “We look for the resurrection of the dead,
and the life of the world to come.” and the Apostles Creed “the resurrection of the body, and life everlasting.” we attest to the hope of resurrection, but nothing is said about human disembodied souls going to heaven…
The Nicene creed was never meant to be an exhaustive list of Christian belief. Just the basics. Christians have from the beginning believed that souls were in heaven already.

but then there is Jesus on the cross telling the thief that today he would be in paradise…
gotquestions.org/today-paradise.html
Anyway… I obviously don’t believe in any of this mythology… but it is fun to read and talk about…
Glad you are here.
To the OP:
I would point your friend to Revelation chapters 5, 6 and 7. In those chapters, John has a vision of heaven as it is right now. In chapter 5:5-8, he sees 24 elders (human beings) worshipping God in heaven and presenting the prayers of the saints on earth to Him. In chapter 6:9, he sees the souls of those who were martyred asking God how long it will be until their blood is avenged. In chapter 7:9-10, John sees in heaven:
"a great multitude which no man could number, from every nation, from all tribes and peoples and tongues,
standing before the throne and before the Lamb, clothed in white robes, with palm branches in their hands, 10 and crying out with a loud voice, “Salvation belongs to our God who sits upon the throne, and to the Lamb!”
All this is before the end of the world and the resurrection of the dead.
Hope that helps.