boot order

[wdt]

In this case, the uboot on the emmc is not playing well with the OS on the SD
There are 2 different boot orders
1st, the boot rom, with limited memory, only that on cpu, searches SPI, emmc, SD
It searches for idbloader at 64 sectors in, for the byte signature, this sets up memory on board
Then, on same media uboot is loaded (now that there is enough memory to load it)
uboot, nearly always, alters the boot order,, for example
strings uboot.img |grep -i boot_target
boot_targets=mmc1 nvme0 usb0 mmc0 pxe dhcp ,,,, (mmc1 is SD, mmc0 is emmc)
uboot searches for boot.scr OR extlinux.conf OR bootaa64.efi

manjaro does have a BSP uboot in its repository, that might work
You do have to manually install it, and do make a backup of extlinux.conf 1st of all
Some of the earlier versions overwrote extlinux WITHOUT making a backup,,
and the new extlinux was incorrect, I don't know if that has been fixed
--edit--
manually install,, packman just puts the files in /boot (idbloader, uboot, trust AND overwrite extlinux))
and you have to then dd them to right place