Yeah, as @jsonbecker has already pointed out, that’s by design when it comes to automatic summary splitting. HTML tags are kept if you do the split manually, though, using the <!--more--> summary divider. So, posting like this should keep the video in the home page’s list view:
It should be noted the micro.blog timeline strips embeds so that post will work on your site, but have the missing video there. That’s true regardless of truncation.