Q.Are coffee grounds good to mix for indoor dirt mix?
What’s a good mix for orchids indoors?
Unfortunately there is some bad advice circulating about coffee grounds. They do not substantially lower the pH for acid-loving plants because whatever acid the beans had originally mostly comes out in the coffee liquid. And not all coffee beans are acidic to begin with. Your best bet is to obtain a potting mix designed for orchids. In addition to having a low pH, it will be a fast-draining mix which orchids must have. Here are two articles on general orchid care: https://www.gardeningknowhow.com/ornamental/flowers/orchids/indoor-orchid-care.htm