As far as I can tell, it's still the case if the video is DRM-ed. Then any screenshots of it will be black square, because the OS can't "see" the video, it's sent directly to the monitor, similar as in the article.
No, it's not that. Usually, the OS does see the video and the compositor still renders it to the screen like normal, but when you take a screenshot, the OS itself is an accomplice here by not rendering that surface in screenshots.
Not true about Android at least — there is secure boot where the bootloader will snitch on you if you unlock it, and you can't do anything about it because the attestation happens in a trusted execution environment, a hypervisor with higher privileges than the OS kernel, that you never get to unlock.
