That's because Nix is busy building the stuff in your configuration.

Since I've shared the output, you don't need to build it yourself and can just import it directly into your store.

I got this

$ /nix/store/mpgh4905nxkpf0jxcx90lchhf6l5gpiq-nixos-system-nixos-23.11.git.7c67f006ea0M/bin/switch-to-configuration boot
File system "/dev/mmcblk1p3" has wrong type for an EFI System Partition (ESP).
systemd-boot not installed in ESP.

In reply to @thefossguy:matrix.org
I noticed that the image (https://github.com/misuzu/nixos-vf2) didn't boot with all combinations of DIP switches so me being extra smart, I dd-ed uboot SPL and SBI firmware on /dev/sda1 and /dev/sda2 respectively and mvoed /boot to /dev/sda3 and / to /dev/sda4. Now, your derivation doesn't work because it expects "/dev/sda1" to be EFI?

In reply to @thefossguy:matrix.org
Ah, so I'll need to build it myself?

I inserted an old SD card (which didn't manipulate the partitions) and now the console complains this:

switch to partitions #0, OK
mmc1 is current device
found device 1
bootmode flash device 1
Failed to load 'uEnv.txt'
Can't set block device
Hit any key to stop autoboot:  0
Failed to load '/uEnv.txt'
## Warning: defaulting to text format
switch to partitions #0, OK
mmc1 is current device
** Invalid partition 3 **
Couldn't find partition mmc 1:3
## Error: "bootcmd_mmc1" not defined
starfive_pcie pcie@2C000000: Starfive PCIe bus probed.
PCI: Failed autoconfig bar 10
ethernet@16030000 Waiting for PHY auto negotiation to complete......... TIMEOUT !
phy_startup() failed: -110FAILED: -110ethernet@16040000 Waiting for PHY auto negotiation to complete....... done