Thanks, any chance you can provide the log lines above the kernel panic? Was this when the init system was loaded already?
Our Trixie and Forky images both ship with identical kernel and setup, only the Debian repo, hence e.g. systemd version, is different.
QSPI → NVME(grub) → USB(Ubuntu240404)
Does this apply to all your tests? The GRUB EFI bootloader in the SPI flash, GRUB configs with boot menu on the NVMe? Was this installed via grub-efi-riscv64 from a Debian system on the NVMe? DietPi Trixie and Forky tested with the same USB stick? And how did you generate the boot menu entries? I wonder e.g. how it knows e.g. the device tree to load, and the cmdline, whether GRUB detects and parses /boot/extlinux/extlinux.conf automatically or so.