RPi4C wont boot with NVMe after executing the guide

I followed the guide to boot from NVMe drive. I wrote the ubuntu image via etcher to the SSD. The SPI is flashed. When I start the RPi4C without SD-Card an SSD attached. The blue light stays blue and does not blink. If I start with SSD and SD. The same thing happens. If I start without SSD and only SD attached the RPi4C boots as expected.

Where do I start do debug?
Can I somehow reset everything and start from zero?

When the SSD was brand new The RPi4C would start with it attached.

After completly deleting everithing from the SSD the RPi4C boots from SD with the SSD attached to it. It seems like the System wants to boot from SSD but it doesn’t work. Right?

I used the dd tool to add the ubuntu image to the SSD. Now booting fails again.