When you view an HTTP resource directly in your browser, Chrome allows it but displays the ‘Not Secure’ message to the left of the URL bar.
When you embed HTTP resources in an HTTPS page, older versions of Chrome allowed that ‘mixed content’ and just displayed a warning in the browser console. Starting with Chrome 85, the browser tries to automatically upgrade the content to HTTPS (if available), otherwise it blocks the non HTTPS content.
Just for testing, you might just try disabling the Mixed Content Blocking in Chrome on the desktop per the linked article just to see if that fixes your issue. If it does, you can decide if you want to leave it with mixed content enabled or if you want to add SSL to your Blue Iris setup.