Send your store url
You have used Youtube video and Youtube video cant auto play in mobile.
For that you have to change video section with html video tag.
Thanks. So I have to change it to a video section? (this seems to only accept a link to youtube / vimeo)
Or, do I use the custom content section and manually add the video? If this is the way, is it possible to style it like the native background video does? (i.e. autoplays, full screen and has a buy now button over the top?). Can you help me with the code for this?
Yes you have to remove YouTube video section and add your custom section with html video tag.
You can follow my this post
We have to do custom code for that if you cant.
Send me your store url.
In this theme video section created by theme in-build so may be you can check if you have option for that in theme editor.