I notice you mention running adb from a container - you may be doing so already but generating an image to flash might sidestep a few setup issues.
Pretty sure there was a similar black screen issue on an early pinephone build which was fixed pretty quickly. Sharing some logs may help them assuming things like adb logcat are working.
Pretty sure there was a similar black screen issue on an early pinephone build which was fixed pretty quickly. Sharing some logs may help them assuming things like adb logcat are working.