Why screen locks while watching YouTube videos?

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I have a Huawei Mate 20 Pro. Up until yesterday the YT behaved normally, that is when I watched a YT video the screen did not lock - as long as the video was being played. Now it first dims, then locks itself. I would need to keep on touching the screen to view anything on YT. I did not change any settings. The only thing I did is connect to a Android-based smart TV, however I did connect to the same TV previously and the behavior on the phone was not affected. Went through settings both in the YT app and the system, but no help there.

System: 9.0.0.153 (EMUI 9.0.0)
YT App: 14.04.53