The plant is buried too low in the soil. All the leaves should be above soil level, and all the roots below. If you can't see the base of the plant, it needs to be higher. Try removing some soil from the pot (rather than unpotting and repotting the plant), so that you don't have to manhandle the roots too much.
The soil also looks too rich. Try using bagged cactus mix, or make your own by combining regular potting soil with an equal amount of perlite, pumice, or equivalent. Regular potting soil can be made to work, but you have to be careful not to overwater.
When you do water, water well (until water comes out the hole in the bottom of the pot) and then wait until the soil is dry at depth before watering again. You can push your finger in a couple of inches, or a bamboo chopstick, or a moisture meter, whatever allows you do get a sense of the soil moisture. The top layer will dry out first and not be an accurate indicator of what's going on at depth. The actual time it takes to dry out will depend on light and temperature and humidity, but through experience you will get a better sense of how this works. Maybe once every 2 weeks indoors with good light, to start with.
Watering is much more straightforward, and the plant will be much more healthy, with strong light. Provide as much light as possible if the plant is going to be indoors, like right in front of your sunniest south-facing window. If the plant can "see" the sun for hours a day, it's got enough light.