Paul was still an observant Jew. He still obeyed Gods Commands. The Mosaic ordinances and ceremonies pointing to Christ were done away with. They were no longer necessary because the Messiah had already come (and the world knew Him not).
The Council at Jerusalem in Acts 15 also addressed the need to eat kosher and follow other parts of the Law.
yes Paul was observant but his converts were not - thus tension with James and that arm of Jesus followers that was eventually clipsed. but the vestiges of Jewish observance by Jewish Jesus followers took some time to drop away as the Church Fathers were preaching against using the Jewish calendar, celebrating J holidays and Shabbat well past 400 CE according to research of Michal Bar-Asher Siegal.