If ums-emmc is not successful, then it’s because something failed when enumerating the eMMC. You can get the exact error with an UART cable: Libre Computer Board Debug Serial UART Connection and Setup Guide
If ums-emmc is not successful, then it’s because something failed when enumerating the eMMC. You can get the exact error with an UART cable: Libre Computer Board Debug Serial UART Connection and Setup Guide