Thanks to Sir Sebastian for requesting this video using a mechanical keyboard with Cherry MX Blue Switches. Hope this is something like what you wanted. The text I'm typing is from the first chapter of 'Dracula' by Bram Stoker.
To listen while using other apps, switch the player to Picture-in-Picture (PiP) during playback — it keeps playing in a small floating window (the screen stays on).
To listen with the screen fully off, in-browser playback stops by YouTube's design. Open the video in the YouTube app to keep listening where background playback is supported (e.g. with YouTube Premium).
Open in YouTube app