Catholics are the fundamental Christians. The rest are sects mostly founded in heresies.
(1) Only the Catholic Church can trace its roots back to Christ Himself.
Within a few short years of the Resurrection, the followers of Jesus began calling themselves “Christians” (cf. Acts 11: 26), and by the end of the first century, the word “catholic”—meaning “universal” —was applied to the Church. The idea of different (and sometimes competing) Christian denominations would have been unthinkable to the early Christians, especially in light of Christ’s pronouncement on one shepherd and one flock (John 10:15) and his prayer that his disciples remain one (John 17:22). It was only human weakness and sinfulness that brought about the religious divisions that afflict Christianity today.
(2) The Eucharist—the Real Presence of Christ—is not found in Protestant churches.
(3) Unlike other Christians, Catholics have a fully sacramental understanding of God’s saving activity.
(4) Because of the Church’s magisterium, Catholics have the assurance that their beliefs are divinely revealed truths, not human interpretations and opinions.
https://www.catholic.com/magazine/print-edition/christian-yesbut-why-catholic