According to relevant data, Kangxi did bow down to Zhu Yuanzhang's mausoleum in history, and more than once. Every time Kangxi went to Jiangnan, he made a special trip to pay a visit to Zhu Yuanzhang's mausoleum, and it was very serious, not furtive, but aboveboard.
One of the fundamental reasons why Kangxi did this was the legitimacy of the Qing Dynasty ruling the Ming Dynasty. Because when Li Zicheng perished the Ming Dynasty, Manchu defeated Li Zicheng and moved its capital here under the banner of revenge for the Ming Dynasty, which actually ruled the territory of the Ming Dynasty. We can see that the Qing dynasty didn't say anything about overthrowing Daming, so if the Qing dynasty didn't worship Zhu Yuanzhang, it wouldn't make sense in jurisprudence and would affect the rule of the Qing dynasty.
Moreover, it is not only Kangxi who went to worship Zhu Yuanzhang, but actually it is very important for the Qing emperor to worship the Ming Tombs. Every generation of monarchs need to worship to show the respect of the Qing dynasty to the Ming dynasty. On behalf of the Qing dynasty, it actually inherited the throne of the Ming dynasty, which is an inheritance relationship. Although it seems a bit far-fetched, that's what the Qing Dynasty did.
It is very important for the Qing Dynasty to maintain this legitimacy. First, it can appease the people's hearts, because although the Ming Dynasty was extinct, the people still paid more attention to Daming, and many things against the Qing Dynasty made the Qing Dynasty feel at a loss. This idea of inheriting the Ming Dynasty can alleviate this contradiction. This is also the need for the Qing dynasty to maintain its own rule, so that the people can see their reverence for the Ming dynasty, win over some clan members, and let the people recognize the Manchu rule.