If people can take probiotics to have more good bacteria, can they take some kind of good fungus?

No: You do not need good fungus for digestion.

Yes, and many do: Fungi are not part of our normal flora but yeast are. Many take Sacchromyces boulardii, a probiotic yeast, often sold as Florastor, esp. useful for preventing diarrhea & yeast infections when taking antibiotics. As for good fungi, medicinal mushrooms such as Reishi, Maitake, Shiitake & Cordyceps have many powerful proven health benefits, but, unlike probiotics, these don't live in our intestines.