Installing OPNsense 25.1-serial-amd64 on DEC677 fails (SOLVED)

[VirtualeXistenZ]

Booting on a USB with the above image.

Logging on with installer and opnsense. Installer starts.

After selecting the default US keyboard you get to choose installation method.

Both the UFS and ZFS option throw an error:

"partitioning error and installation step has been aborted. Would you like to restart the installation ..."

What I have done so far.

Tried different methods of writing the image. Rufus and dd.

# dd if=/dev/zero of=/dev/mmcsd0 bs=1M
# gpart destroy -F mmcsd0

# camcontrol devlist
(only lists my USB. I expected it to also show the DOM)
<Kingston DataTraveler 3.0 PMAP>  at scbus2 target 0 lun 0 (pass0,da0)

Can I add an NVMe and use that instead of the "faulty" DOM, or could there perhaps be another solution?

*****
Update 1
Installed in expert mode. Showed the DOM.
Deleted the disk and created a GPT.
Created a UFS boot environment. Installed ... took a while though.
Rebooting is stuck in "Booting from Hard Disk..."
*****
Update 2
Ejected the SD card. Low level formated in Windows with FAT32.
Copied it full of files with no errors.
Put in a new SD card.
Installing OPNsense on the *new* SD card. Everything is running smooth.
No errors.
Bad SD card? ... but it was OK in Windows. Bahhh...