Udemy Videos are black and unable to see

As described, you are presumably using Apple’s Sidecar feature to use your iPad as a second monitor for your Mac computer.

As such, your own issue is unlikely to be directly related to HDCP - as this copyright protection technology applies specifically to HDMI connections between a source and monitor. HDMI ensures that everything within the HDMI connection chain is HDMI-compliant - and that there are no high-resolution recording devices within the HDMI chain that can extract copyright content.

That said, Apple (as a content provider in its own right) is known to strictly apply copyright controls. It is possible that other measures will influence the ability to stream video content to another computer (i.e., your iPad).

While you may not be able to resolve your current difficulty with streamed video content being forwarded to your iPad via Sidecar, you perhaps have two viable alternatives:

1) Simply stream the Udemy video from the iPad - instead of using Sidecar.

2) Consider connecting your Mac to an actual external monitor - instead of reliance upon Sidecar and its limitations.

Clearly, option #1 will have no negative impact at all upon your limited (solar derived) power budget - as you are already using the iPad in addition to your Mac. However, without having appropriate account credentials to access Udemy content, you will have an ongoing problem.

Perhaps you should seek advice from your company IT Team as, presumably, they will have access to the necessary account credentials - or may be able to offer assistance with bona-fide access to this licensed material.