1. On the latest iOS, Safari, open target video (not via YouTube app) 2. From that video, open any video that’s offered under the target 3. Quickly perform the following: go back to the target and at the same time switch to the next tab in the safari browser (use swipe to switch).

Video should keep playing in the background, even when you lock and turn off the screen.

I also use uBlock origin / DNS blocking.