According to the Ancient Chinese Gender Chart, if your wife is conceived in one of the following time periods in rest time of 2021, you have more chance to get a baby boy:
Apr 12 - May 11 (34 lunar years old, the 3rd lunar month) Dec 04 - Dec 31 (34 lunar years old, the 11th lunar month)
Apr 12 - May 11 (34 lunar years old, the 3rd lunar month)
Dec 04 - Dec 31 (34 lunar years old, the 11th lunar month)