If you are on a modern Mac (Intel or Apple Silicon), the built-in USB port on the Radium 49 likely won't work because the driver won't load. However, the Radium 49 has a standard on the back.
This driver is confirmed to work on OS X 10.8 through 10.10 Yosemite for some users. m-audio radium 49 driver mac
Any macOS from 10.11 El Capitan through the latest macOS 15 Sequoia is not officially supported. The Best Workaround: Using a MIDI-to-USB Interface If you are on a modern Mac (Intel