[BlueDragon]

As you said;

A Crucifix is a necessary element of Catholic Christian prayer.

The Apostles preached "Christ, crucified" for the sins of man, the sin of the world (including those not "Jewish").

They did not preach praying to crucifixes.

From liturgy, widespread in Christian expression;

He is Risen
He is Risen indeed

So -- don't pray to crucifixes. Instead, do as the one who was crucified for our sins directly instructed us to do (when we pray) addressing the Creator directly, in His [the Christ's] name.

Christ is now seated at the right hand of the Father. He did ascend. There were witnesses.

[ebb tide]

Christ is now seated at the right hand of the Father. He did ascend.

From the Baltimore Catechism No. 3; Lesson 4

Q. 917. What is the Mass?

A. The Mass is the unbloody sacrifice of the body and blood of Christ.

[annalex]

don't pray to crucifixes

Don't teach me. I can read the Holy Scripture; I pray as the Holy Church of Christ has taught me.

You got the point that an ecumenical service between the Protestants and the Catholics Christians would be a theological impossibility?