When problems are encountered indoors, the main issue, or at least a contributing factor, is almost always too little light. The indoor environment is dark compared to outdoors, but we don't notice because our eyes quickly adjust.
So put it right next to the sunniest window you have, where it will get the most direct sunlight. Don't worry about temps, as long as you're in normal house temps, it's fine. It's also nearly impossible to give a tree too much light indoors.
The other issue could be drainage/soil. That soil looks pretty poor. I'd recommend repotting using a bonsai soil. Something inorganic (or mostly so) like this.
The tree doesn't look terrible, so repotting now should be ok. But i'm not super familiar with the species, so I can't fully endorse repotting now. Whenever you do, I would mess with/prune the roots as little as possible to reduce stress on the already sick tree.
Good luck.
I don't have a brand preference. I bought some off of Amazon earlier this year that worked well. Here's the link: Bonsai Soil Mix - Premium Professional, All Purpose, Sifted and Ready To Use Tree Potting Blend In Easy Zip Bag - Akadama, Black Lava, Pumice & Charcoal -"Boons Mix" (1.25 Dry Quart) (2.5 Quart) https://www.amazon.com/dp/B01N7KCO5T/ref=cm_sw_r_cp_apa_i_eYZoDbRTG4KJE
I also made my own batch a few weeks ago that turned out well.
Here's a link to an excellent blog about bonsai soil. Very informative: https://adamaskwhy.com/2013/02/01/the-much-anticipated-long-promised-long-winded-ever-lovin-bonsai-soil-epic/
Less Perlite, more rock. The Perlite will eventually work its way upward as you water