In openSUSE MicroOS based images, ignition is used for configuration.
It works by waiting for a block device with "ignition" in its label, which is
usually a usb drive.
Currently there is no usb support on RPi4 in the initrd phase as the
pcie-brcmstb module is missing.

This diff to dracut might fix it, but not tested yet:

diff --git a/modules.d/90kernel-modules/module-setup.sh
b/modules.d/90kernel-modules/module-setup.sh
index 3dfceff0..0ad01112 100755
--- a/modules.d/90kernel-modules/module-setup.sh
+++ b/modules.d/90kernel-modules/module-setup.sh
@@ -35,6 +35,7 @@ installkernel() {
             "=drivers/input/keyboard" \
             "=drivers/usb/storage" \
             "=drivers/pci/host" \
+            "=drivers/pci/controller" \
             ${NULL}

         instmods \