There are multiple Christian beliefs that are incompatible with Judaism:

1. The belief that God is multiple entities rather than a single entity.
2. The belief that God was ever physically embodied in human form or is a parent not just metaphorically of all people but literally of an individual.
3. The belief that humans are born with “original sin” rather than innocent.
4. The belief in eternal damnation and the need to be “saved” from it.
5. The belief that belief in God, alone, is sufficient for forgiveness (rather than the process of teshuva, repentance). Further, the belief that God is capable of forgiving transgressions between people.
6. The belief that the Torah is obsolete/replaced and no longer valid.
7. The belief that statues of Jesus, Mary, saints, and other such symbols are permissible in worship; in Judaism, this would be considered idolatry.
8. The belief that death is a good thing and the general symbology associated with death, the crucifixion, etc.; Judaism is about the primacy of life and lifesaving, and the obsession with the macabre in Christianity is culturally foreign from a Jewish standpoint.
9. The belief that there were prophets after Malachi.
10. The belief that there is a “New Testament” that is valid and divine.
11. The belief that life begins at conception and that abortion is murder; in Judaism, life begins at birth, and abortion is the destruction of potential for life, not actual life, with it not only permissible but religiously mandatory in the case where it is necessary to save the mother’s life.
12. The belief in the duality between God and the Devil, and the related idea that an angel can somehow oppose God and act against the divine will. In Judaism, angels lack free will (it is one way in which angels and humans are distinct), and the satan is not a specific being but a title/role of a being that is effectively a cog in the wheel of divine justice (it is the moral equivalent of the District Attorney in bringing charges against those who act unjustly, not tempting or causing people to behave that way). The idea that world events are caused by opposing forces (God & the Devil) vs there being only one force (God) is polytheistic from a Jewish lens.

These and other things are just a few forms of incompatibility.

Related answers:

• My answer to Can the Abrahamic religions be considered one religion?
• My answer to Is there really a difference between Judaism, Catholicism and Christianity?
• My answer to Can you be Jewish and believe Jesus is the Messiah also?
• My answer to Why don't Jews try to convert people like Christians do so they can share the truth and get more followers?
• My answer to Is it possible to be Jewish and Christian at the same time?
• My answer to Why is it that a Jew who becomes atheist is still considered Jewish, yet for a Muslim or Christian, it is different?
• My answer to Can a Jewish person enter a church for a nonreligious purpose like a chorus concert?
• My answer to Do you think Islam and/or Christianity are culturally appropriating Judaism? Or is it cultural appreciation? Or neither? Why?
• My answer to Is the phrase "Judeo-Christian values" accurate, when they actually describe core Jewish values that Christians have merely adopted?
• My answer to Do any aspects of Judaism accept Jesus as the Messiah?
• My answer to Is the main difference between Judaism and Christianity the prophet in which they believe? Did both religions hear God speak from the mountain top?