2013 Hyundai Sonata radio works when it feels like it

Have standard radio. Radio will work at times. Took to dealer, said found loose connection at fuse box. worked for a few days and radio quit. Will work when it feels like it.

It sounds likely that the fuse box repair did not hold up. Take it back.

^ This. But the “loose connection” may not be the only problem. There could be an internal fault in the radio. If the shop tells you the original repair is good, or if they fix it again and the problem comes back, you may have to start looking for another cause.