Is it illegal to officially sell the same strap as Apple?

Illegal. According to the law of network display. Without the authorization of Apple, selling a watchband that is the same as or similar to Apple's official watchband involves infringement of Apple's trademark rights, patents, copyrights and other intellectual property rights, which constitutes infringement. Therefore, when selling similar products, we must first understand the relevant laws and regulations and the protection of intellectual property rights, and try to avoid infringing on the intellectual property rights of others.