Carefully placing an artfully-shaped bonsai tree on your desk might make you the envy of your coworkers who see it during Zoom video calls, but to keep it on display there healthy, long-term, you'll want to choose the tree species carefully.
It’s unlikely you have perfect plant conditions in your office or home work-space; most indoor environments stay at low-humidity and 68-75 degrees Fahrenheit (20-22 degrees Celsius). Unless you're in the lucky minority with a lot of natural light in your office, you probably work under artificial lights - fluorescent, LED or incandescent. While these temperatures and lighting conditions are great for human comfort, they're not the ideal environment for bonsai growth.
Here's a list of species that can thrive indoors. These are adapted to constant-moderate-temperature, low-humidity and low-light conditions, and likely native to mid-elevation dry tropical forests.
Watering - watch the soil and only water when it starts to dry out. Watering from above flushes salts from the soil that can build up over time, and watering by soaking makes sure all the soil gets completely wet. Alternate the two methods for best results.
Fertilizer - use nutrients like DynaGro, Miracle Grow or a time release like Osamcote. These are all salt-based fertilizer that will not cause odors, and will give your plant lots of nutrients to keep growth going.
Light - optimize the light. Depending on your location the angle of the sun may change significantly through the year (and through each day, too.) Move your bonsai around weekly or monthly to make sure it’s getting good light. If light is strongly from one direction, be sure to rotate the tree every couple weeks also.
Pests - Keep your eye out for anything that looks like a tiny insect - black bumps, green bumps, white flies, aphids and the like. Spray them or wipe them off and use a contact-spray insecticide (there are different kinds for different species.)
Dormancy - if you choose to keep a non-tropical plant inside for a while, it’ll usually do fine. But, make sure that you give it some cold dormancy. Junipers can be placed outdoors for winter where temperatures will not drop below 28 degrees Fahrenheit. Or you can keep them in your unheated garage or another space where it is cold (30-45 degrees Fahrenheit) but not freezing for a couple months in winter. Some plants go dormant based on temperature and others go dormant based on day-length; to be safe, provide both cold temps and short days for these plants at the same time - during winter.