Since 2017 new policies web browsers no more allows autoplay for unmuted videos. This is why we muted all background videos by default and users can’t control it in the block settings.
There is an article in Chrome blog with more info https://developer.chrome.com/blog/autoplay/:
Web browsers are moving towards stricter autoplay policies in order to improve the user experience, minimize incentives to install ad blockers, and reduce data consumption on expensive and/or constrained networks. These changes are intended to give greater control of playback to users and to benefit publishers with legitimate use cases.