Paul had Timothy circumcised to enhance Timothy’s acceptance and effectiveness as a Jew in Jewish circles. This was not the same as Titus, who was a full Gentile ("Greek"; Galatians 2:3).
Elsewhere Paul clarified that it makes no difference to God whether one is circumcised or not circumcised (Romans 2:25–29; Galatians 5:6; 6:15). Paul was prepared to use any legitimate means to communicate the good news about Jesus to different audiences (1 Corinthians 9:20–21).