Regretfully, we can not download the Xubuntu Core 21.10, today*. Instead you will use a torrent for Xubuntu Desktop 21.04. When using MacOS X, Free Download Manager or its compatibles must be prepared on your Mac. By clicking the downloaded torrent, iso-file will be downloaded on your Mac. Using this image file, you can make a bootable USB disk using balenaEthcer.
After making a boot disk for Xubuntu Core, turn-on your Mac while pressing on the option key. Then this screen will be appeared on your monitor.
Please select right hand side disk and tap return key. Then you can see a boot-selection window on screen as follows. You can choose the language of your country. Here we chose "english".
Choose the keyboard layout. Here we chose "english".
Then you can choose the installation manner of Xubuntu system on your HDD/SSD . It is easy for non-experts to choose "Erase disk and install Xubuntu" as follows.
It is important for a music player to choose the "minimal installation" of Xubuntu that finally almost compatible with Xubuntu Core.
*I prefer Xubuntu Core 21.10 for players, however, it is not available today. Only Xubuntu Core 22.10 can be available. The version 22.10 is not good for music players. The sound of 22.04 is too strict and too hard to listen. So you can make a music player by the above mentioned method. Please try! If you are willing to get old iso disk image for Xubuntu Core 21.04, you can email me at anytime.