The eMMC works in the operating system when I boot from the SD card.
However, if only the eMMC is installed, U-Boot is not able to read it.
From the UART screen
Scanning for bootflows in all bootdevs
Seq Method State Uclass Part Name Filename
--- ----------- ------ -------- ---- ------------------------ ----------------
Scanning global bootmeth 'efi_mgr':
Card did not respond to voltage select! : -110
unable to select a mode: -5
Cannot persist EFI variables without system partition
Scanning bootdev 'mmc@ffe07000.bootdev':
unable to select a mode: -5
unable to select a mode: -5
unable to select a mode: -5
unable to select a mode: -5
Scanning bootdev 'mmc@ffe05000.bootdev':
Card did not respond to voltage select! : -110
U-Boot version
=> version
U-Boot 2025.07+ (Sep 04 2025 - 17:43:40 -0400) Libre Computer AML-A311D-CC Alta
aarch64-elf-gcc (Linaro GCC 7.5-2019.12) 7.5.0
GNU ld (Linaro_Binutils-2019.12) 2.28.2.20170706
Not sure about the default in the u-boot driver but it could potentially be 8 lines in u-boot and 4 in Linux. Please have them ship you another module.