Q.Mint Cultivation Indoors
Whenever I try to grow mint indoors in my apartment, I place the potted plant in a south-facing window, but the plants always grow thinly, with leaves small and wide apart on the stems.

Certified GKH Gardening Expert
It sounds like there is, simply, not enough light in the area. I would opt for a grow light! Mint will be very forgiving on the type that you use.
Here is an article that will help:
https://www.gardeningknowhow.com/houseplants/hpgen/fluorescent-lighting-for-indoor-gardening.htm