Hello @GeoffM54 ,
The video block in the cross-device/platform editor allows for other video hosting sites, however they still need to be compatible in a way that procures a thumbnail via embed.ly, which is typically only applicable to dedicated video-hosting sites. Keep in mind that videos aren't embedded into emails, they're linked to. The video block is essentially an image block, with an auto-generated play button on top of the thumbnail info provided by the host site.
If a link to a video you're trying to add isn't compatible with the video block, then I'd advise using one of normal linking methods:
Text links
Image links
Button links
... View more
