Android - Prevent phone from sleeping while watching fullscreen video

Hello, I have an Android Pixel 3 XL. When someone uploads a video, I can tap to play it and then tap again to view it in an expanded full screen view. If the video is longer than 30 seconds, my phone will go to sleep while I am watching the video, even while in the full-screen expanded view. This is frustrating because I don't expect it to behave this way.

My suggestion is that watching a video in this expanded view should prevent the phone from sleeping, like for instance the YouTube app does. Thank you.