Bob says 'Hi' - The tag does say that he's an indoor plant but with further reading, I have found that he could be an outdoor plant if conditions are favourable.
He looks like he's enjoying his spot on my shelf though so I'm happy if he's happy
There are no "indoor" plants. Only plants that can tolerate being indoors to varying degres.
Tropical species can sometimes fit the bill, particularly ficus and schefflera.
Indoor conditions are pretty stressful for any plant. Extremely low light (even with supplemental "grow" lights), extremely low humidity levels (lower than a desert's with air conditioning and/or central heating) --humidity trays do VERY little to help and can actually make things worse if the tray holds enough water to come in contact with the bottom of the pot, which can keep the soil soggy. The only way to reliably and effectively provide humidity is to dedicate a room and get a humidifier for the entire space, which can lead to other problems like mold. Air circulation is critical also, as indoor plants tend to develop mold and spider mites. A small fan set on low directed at the tree would help.
The optimal solution for indoor plants is to put them outside for half the year, from late spring (once frost danger has passed) to autumn (back in before frosts arrive). That gives the plant a chance to recharge and grow without the stress. The tree will limp along inside until the spring comes again using the resources it stored up when growing outdoors.
Keeping bonsai inside greatly complicates the entire learning curve for bonsai, forcing people unfamiliar with bonsai to also learn how to care for a houseplant along with bonsai needs (some needs are similar, but others not so much)
FWIW, I've found Australian brush cherry becomes very unhappy being inside all the time. They lose all of their leaves over a few months, then sulk until they die or become shadows of their former selves. Sorry...That's been my experience. I had two of these when I started over 20 years ago.
Of course if you have no "outside" options, you're stuck and have to deal with the situation. Best place for the tree is the brightest spot in a room Windowsills are not the greatest place, as they can be drafty in the winter, and intensely hot in the summer.