Unable to boot without a monitor plugged and turned on :/

Hi everyone,

I made this little LENOVO Thinkcentre m910q (i5 6500T - HD 530 - 8/256go - Intel combo WiFi/BT) running smooth with Monterey 12.6.7 (OpenCore 9.5)) that I got for 35€.
Everything works but:

I would like to plug it to my box as a mini server with an automatic bootup/shutdown via pmset.

Unfortunately, I'm unable to turn it on if no screen is attached and turned on.
It boots without password request and screen sharing is turned on, but I'm unable to boot without a screen, I don't know where the problem is.
Intel HD530 was a mess to setup but it works well with full acceleration/metal support.

I don't know where to start, any suggestion that can help will be welcome !

THANKS