Muted video not autoplaying in mobile

Question

I have a Youtube video that I want to autoplay on my homepage.

https://www.imaritouen.co.jp/newhome/

I understand that mobile browsers limit autoplay unless the video is muted. My embed code looks like this:

<iframe src="https://www.youtube.com/embed/RT5ijayFPh0?controls=0&modestbranding=1&autoplay=1&mute=1&playlist=RT5ijayFPh0&loop=1" allow="autoplay"></iframe>

The video will autoplay on desktop but not mobile.

I've read a number of blogs and threads on here, including:

https://developer.chrome.com/blog/autoplay/

https://github.com/videojs/video.js/issues/5233

Youtube embedded video: autoplay feature not working in iphone

Youtube autoplay not working on mobile devices with embedded HTML5 player

What am I missing?

EDIT: The settings on my Android browser allow autoplay on muted video.