As for religion, I have recently read some things about buddhas and bodhisattvas, and I am a little interested, but I don't understand why monks should abstain from sex.

This is a profound truth. Let me make it clear for you, for example.

First, the central idea is that the Buddha said that "all living beings have the wisdom and virtue of the Tathagata, but only because of persistent delusions." A superficial understanding of this sentence is that "everyone has Buddha nature, and everyone can become a Buddha." Suppose the Buddha is a crystal-clear light bulb, which can emit 100 watt of light, then we mortals are also a light bulb, because the light bulb is contaminated with a lot of dirt. Therefore, although there is a basis of 100 watts, it can only emit 20-30 watts of light. Only by wiping off these dirt, it is possible to emit 100 watt light. This erasing action is called "practice", and the person who cleans these dirt is called "Buddha". In order to help everyone practice, the Buddha divided these filth into three categories and named them. Buddhists are divided into professionals (monks) and amateurs (family members), so monks should abstain from color.