This should be seen in stages. A long time ago, when an individual registered a trademark, the category of the trademark should be consistent with the main business. Of course, it was a long time ago, and then the trademark law was amended. There is no such restriction now.

Another point is that trademark registration is beneficial to the same as the main business. Otherwise, if you register this trademark, you have to use it in your main business, right? This requires the trademark to be consistent with the main business, otherwise it cannot be used in the main business.