Didn't the Qing dynasty cut off the Hanfu of the Han people? Why do people still wear Hanfu in ancient paintings of the Qing Dynasty?

You can't. When the Qing Dynasty just ruled China, wearing Hanfu was not allowed to have long hair, otherwise it was beheading. So you can't wear it.

1644, the Qing army entered the customs, occupied Beijing, and attacked the regimes of Nanming, Dashun and Daxi. At the same time, the policy of shaving hair and changing clothes was fully implemented in the occupied areas, forcing all officials and men to change Manchu hairstyles and wear Manchu clothes, and it was forbidden to wear Ming Dynasty clothes. Those who didn't want to shave their heads were even put to death during the Shunzhi period in the early Qing Dynasty. However, in the second year of Shunzhi, it was promised that "it is easier to wear clothes", so the people still wore clothes from the Ming Dynasty. Even when the Qing dynasty strictly enforced the order of shaving and changing clothes, the objects they could really master were only Han Chinese officials, while the vast rural areas were beyond the power of the Qing dynasty. Therefore, it was also popular in the early Qing dynasty that "the official surrendered to the people and did not surrender." Because the struggle lasted for many years, it was difficult to enforce the law. With the stability of the Qing regime, the law enforcement of shaving and changing clothes was obviously relaxed. During the Kangxi period, many civilians in the south of the Yangtze River still wore Ming Dynasty-style clothes such as wide robes, big sleeves and right collars. In the prosperous scene of Suzhou during the Qianlong period, some farmers in the south of the Yangtze River still retained the style of the late Ming Dynasty in their costumes.

The hairstyles and clothes of the characters in the forty-six ploughing and weaving pictures drawn by Jiao Bingzhen in the thirty-fifth year of Kangxi in the National Palace Museum in Taipei are all old works of the Ming Dynasty. Jiao offered sacrifices to the imperial court during the reign of Kangxi, got to know western missionaries who came to China to preach, and studied western sketches. Therefore, the positions of landscape figures and terraces he painted are from near to far, arrogant and uncomfortable. The village scenery, family farming, people's clothing and hair accessories in its farming map should be quite true. Moreover, the plow weaving map was published only after Emperor Kangxi saw it, and it was called "purport", indicating that Emperor Kangxi approved the clothes of the characters in the map. It can be seen that the hairstyles and clothes of rural gentry and peasants in China during the Kangxi period had been restored to the old by the Ming Dynasty. Moreover, the Han women in Qing Dynasty could wear the decorations of Ming Dynasty, which further influenced the aesthetics of Manchu women. You can also refer to the twelve beauties of Yongzheng.