Paul did speak to the Gentile churches on the Sabbath...
In Antioch...
Act 13:42 And when the Jews were gone out of the synagogue,
the Gentiles besought that these words might be preached to them the next sabbath.
Act 13:43 Now when the congregation was broken up, many of the Jews and religious proselytes followed Paul and Barnabas: who, speaking to them, persuaded them to continue in the grace of God.
Act 13:44 And
the next sabbath day came almost the whole city together to hear the word of God.
That would be the Gentile city of Antioch.
In Phillipi...
Act 16:12 And from thence to Philippi, which is the chief city of that part of Macedonia, and a colony: and we were in that city abiding certain days.
Act 16:13
And on the sabbath we went out of the city by a river side, where prayer was wont to be made; and we sat
In Thessalonica...
Act 17:1 Now when they had passed through Amphipolis and Apollonia, they came to Thessalonica, where was a synagogue of the Jews:
Act 17:2 And Paul,
as his manner was, went in unto them, and
three sabbath days reasoned with them out of the scriptures,
Paul's manner was the Sabbath.
In Corinth...
Act 18:1 After these things Paul departed from Athens, and came to Corinth;
Act 18:2 And found a certain Jew named Aquila, born in Pontus, lately come from Italy, with his wife Priscilla; (because that Claudius had commanded all Jews to depart from Rome
and came unto them.
Act 18:3 And because he was of the same craft, he abode with them, and wrought: for by their occupation they were tentmakers.
Act 18:4
And he reasoned in the synagogue every sabbath, and persuaded the Jews and the Greeks.
Every week on the Sabbath.
Now if Paul really did not keep the Sabbath...
Act 23:8
For the Sadducees say that there is no resurrection, neither angel, nor spirit: but the Pharisees confess both.
Act 23:9 And there arose a great cry:
and the scribes that were of the Pharisees' part arose, and strove, saying, We find no evil in this man: but if a spirit or an angel hath spoken to him, let us not fight against God.
do you think these guys would have said they found no evil in Paul? They would have stoned him on the spot if he broke the Sabbath and taught others to.