There are also other similar techniques (besides Natural Cycles) called FAM, Justisse, or natural family planning, where you can take courses and learn to identify your fertile days. They work similarly to Natural Cycles with temperature tracking and menstrual cycle charting to see your individual patterns.
Often, the charting is done manually with a calendar, for example. You can also learn to identify when you are fertile by looking at fertile mucus and the position of the cervix. But it requires some learning.
For some, Natural Cycles may work less effectively if they have a low body temperature and rarely reach 36.8°C or if they have irregular patterns that the algorithm has difficulty recognizing. In that case, it may be better to look into Justisse, FAM, and similar methods.