In the afterlife, is one still a human? Or is an angel (or whatever you are after death) something other than a human? Obviously, according to Christian views you would not be an animal, but would you still be a human?
Scripture does not term the matter the way you are terming it. Scripture speaks of 'souls under the altar' for example, (Revelation 6:9).
Only mankind have souls. (Angels do not, they are 'spirits'.)
And the soul is immortal, '... whosoever liveth and believeth in me shall never die', John 11:26.
Those who are 'born of water and of spirit' and 'born from above' (anothen) and 'born anew' (anagenesis) and 'born again' (paligenesis) and 'born of God', are members of Christ and are members of a new humanity.
That humanity will come into full realisation (a matter of sonship and full redemption and full restoration) in resurrection.
Then, there shall be new heavens and a new earth (see Revelation 21) to accommodate the new humanity.
Till then, the redeemed are one with Christ in Spirit (but still in the body of sin and death, pending resurrection, though not held by the power of it, by faith in Jesus Christ).
Do You Remain a Human after Death?
A human being while living on earth is considered to be a rational animal composed of a physical human body and an immortal soul. At the moment of death, man ceases to remain a human being in the strictest sense, since man in his human body is separated from his soul.
The nature of human-kind considered abstractly and apart from its elevation by grace to a supernatural state with a heavenly destiny. It is the human as such, having a body and soul, capable of rational thought and voluntary decision. Actually human nature has never existed independent either of a supernatural destiny or of free acceptance or rejection of the super-natural invitation of God's grace.
Up until the general resurrection on the last day those in heaven or hell would be more aptly called persons, just as angels would be, although not being angels but immortal souls.
"An individual substance of a rational nature" (Boethius). Therefore every individual intellectual substance which is complete in itself, uncommunicated and existing for itself, is a person. Essential to person in theological terms are intelligence and substantiality, wholeness in oneself and especially individuality. From individuality flow such features of personhood as distinctiveness, incommunicability, and uniqueness. Among human persons there are also the elements of responsibility and possession of distinctive rights.
It is only after the resurrection of the dead that the souls in heaven (or in hell for the damned) will once more be united body and soul and become fully human again.
Once our bodies and souls are reunited in heaven the Catholic Church teaches that our bodies will be glorified and possess the following qualities: impassibility, subtlety, agility and clarity.
Sacred Scripture and Catholic theology teaches that our glorified resurrected bodies will experience four properties as an outflow of the beatified soul enjoying the vision of God’s essence:
Impassibility – the glorified body will no longer suffer physical sickness or death, as Saint Paul teaches regarding the glorified body in 1 Corinthians 15:42, “It is sown in corruption, it shall rise in incorruption.”
Subtlety - meaning that we will have a spiritualized nature in the sense of a spiritual body as did our Lord as we learn at 1 Corinthians 15:44: “It is sown a corruptible body, it shall rise a spiritual,” i.e. a spirit-like, “body.” We see that Christ’s glorified body was able to pass through closed doors.
Agility – the glorified body will obey the soul with the greatest ease and speed of movement as we read in 1 Corinthians 15:43: “It is sown in weakness, it shall rise in power,” that is, according to a gloss, “mobile and living.” Saint Thomas Aquinas says, “But mobility can only signify agility in movement. Therefore the glorified bodies will be agile.” We discern agility our Resurrected Lord’s ability to bilocate and travel great distances in an instant.
Clarity – the glorified body will be free from any deformity and will be filled with beauty and radiance as we read at Matthew 13:43: “The just shall shine as the sun in the kingdom of their Father,” and Wisdom 3:7: “The just shall shine, and shall run to and fro like sparks among the reeds.” Here clarity refers not being “clear” but to being “bright.” St. Thomas Aquinas at Summa Contra Gentiles, IV, 86 summarized: “thus also will his body be raised to the characteristics of heavenly bodies — it will be lightsome (clarity), incapable of suffering (impassible), without difficulty and labor in movement (agility), and most perfectly perfected by its form (subtlety). For this reason, the Apostle speaks of the bodies of the risen as heavenly, referring not to their nature, but to their glory.”
The best answer is to be found in Paul's "planting a seed" analogy;
"What you sow does not come to life unless it dies. And what you sow is not the body which is to be but a bare kernel" (1 Corinthians ch15 v36, RSV). "So it is with the resurrection of the dead. What is sown is perishable, what is raised is imperishable" (v42).
In that seed-to-plant image, we can see that there is a difference between the seed and the plant, but also a continuity. The moral is that there will be a difference between our present condition and our future condition, but there will also be a continuity.
In Revelation, angels are listed together with elders (5:11)
I looked again and heard the voices of many angels who surrounded the throne and the living creatures and the elders.
and the multitude of people (7:9,11)
After this I had a vision of a great multitude, which no one could count, from every nation, race, people, and tongue. They stood before the throne and before the Lamb, wearing white robes and holding palm branches in their hands. . . .All the angels stood around the throne
thus showing they are different from the multitude and the elders, who remain human.
Yes, one is still a human in the afterlife. Human disembodied souls, while spiritual, are esentially different from angels. Angels are spiritual beings who are created to be purely spiritual whereas human souls are created to animate a human body. Even if a human soul subsists after separating from the body, it is "incomplete" because it has not been created to be in that state. That's why the divine work of salvation is complete only at the resurrection.