Minimal setup to reproduce error
- raspberry pi 400
- official power supply
- no SD card
From the pi forums, I expect that without an SD card the green LED would blink four times to indicate that it can't find start.elf.
I also tried installing the SD Card bootloader on the micro SD card with no luck - no power light or any other light behavior.
My full setup is
- Raspberry pi 400
- 128 GB SD card flashed with rpi-imager to raspbian
- official power supply
- 2 m micro HDMI to HDMI adapter.
Thanks for reading and for any help you can give!