I’ll try to help you, ivano290….
for the record vinyls from mixer and turntable, you’d need a 2 RCA plugs( male) , plus 2 rca adapter female both ends, to either USA-A male plug or USB-C male plug, and set audio input to USB audio either with Audio Midi Setup or by holding down “option” key while clicking on speaker icon at the top of your screen… the usb-c one is sold on Amazon,
”Vention” is one of the brand names /makers.. gold plated would be better to use, perhaps… same for 2 rca male to USB-A ( don’t forget to get as well 2 rca adapter with female on both ends—a coupler/extender??) for Garage band, look at their faq/troubleshooting sections … I think is Apple product so maybe contact them…
John B