Let me help you with this.
The reason why you are having problems sending CEC commands through DP is that DP natively does not support this feature and I would assume that is why you are using the DP to HDMI adapter.
However, it is important to check the adapter. Passive adapters are very; let’s call it, very simple therefore you can try with an active adapter. We do not recommend the usage of adapters because can interfere in the data transfer and video signal and we cannot guarantee the correct functionality of the device but you can give it a try.
Thanks for your response. I ordered both a direct DP/HDMI cable as well as an active DP/HDMI adapter. The screen works fine, but once again, CEC signals fail to reach it. In addition, while using the passive adapter, the CEC chip installed in the NUC was able at least detect the screen. With the two new cables, it can't. Any advice?
The thing is that even using a cable DP/HDMI the CEC feature is not supported because the signal is sent from the motherboard as DP so the feature is still not available. It is necessary to have an HDMI output from the motherboard to have the CEC commands working.
It is possible to configure the motherboard to send HDMI signals through the DisplayPort?
The CEC commands is a HDMI feature so this is part of the HDMI controller and I regret to say it is not possible to configure it from the motherboard.