Host OS on Raspberry PI 4 keeps restarting unless i connect an external screen

Hei,

I have a weird problem. On my raspberry pi based hassio installation i have an adguard addon and a static ip and dns configuration. It has an integrated deconz zigbee board. I also have a decent power supply for the 4 that delivers 4A.
it seems that the host os is unable to start and keeps restarting unless i connect an external screen. then it starts clean without a problem.
Is there any way to investigate the startup logs from the failed startups? Obviously i can’t connect a screen since then it works. I looked at the sd card but couldn’t find a log file in the boot disk partition. Any other ideas?

Thanks
Jan