**There was no Church North of the Alps at the time of the NT, the only places the NT Church existed in Europe was Italy and Greece.**
Asia minor (modern day Turkey), where all seven churches of Revelation were located, was not Greece. Acts 8 shows an Ethiopian eunuch receiving the message of Jesus Christ and the conversion he commands, who took the gospel back to his home country. Paul’s conversion happened in Damascus, Syria, where the church was already established.
And of course the church was begun in Jerusalem.
Yes, Acts 2 at Pentecost, in Jerusalem, but it like everything in the near east, Greece and Italy was part of the Roman empire. The first Christians were largely Jewish converts, The Eunuch in Acts was an early Convert but there was no Church founded in Ethiopia at the time of the NT, Christianity did reach Ethiopia early that is correct.
Greek Churches would be Corinth (Acts 18:1), Athens (Acts 17:1), Philippi (Saint Paul’s Letter to the Philippians), Thessalonica (Acts 17:1), Crete (Greek Island, Titus 1:5). Cenchrea is another NT Greek Church (Romans 16:1).
In Italy, the Church at Puteoli (Acts 28:13-14) and Rome (Romans 1:7) indicate a thriving Church in both places and the Church of Rome even before Paul got there having an orthodox faith that is admired all over. At Pentecost, there were people from Rome who heard Saint Peter preach and thus Catholic Scholars have long suggested that these early Roman Christians that Peter evangelized went back to Rome and within 10 years, around 42 AD Saint Peter went to Rome where he governed, built up and led the Church. Paul joined him and both were martyred in Rome in the 60’s AD
So even at the time of the Council of Nicea among the 318 Bishops, the only Latin-Roman Bishop at the Council in 325 AD that was from North of the Alps was a Bishop from Southern Gaul (modern France), the other Roman-Latin speaking Bishops were from Italy (Calabria), Roman-Libya, and Spain (Hosius of Cordoba who led the Council), a Latin Bishop from Illyricum (modern Serbia-Alabania, etc) and 2 Roman priests who were the Popes’ personal representatives.
As such, all the regions North of Italy from Poland (inclusive) all the way to the land of the British Isles (Wales, England, Scotland, etc) were evangelized by the Church of Rome. Thus, all that you folks whose ancestors came from North of the Alps with respect to orthodox Apostolic faith you received from the Catholic Church.
East of Poland was evangelized by Churches in the Eastern Roman empire.