In the Webflow designer, you’d assign a class to your embed element, and then at e.g. mobile-landscape you set its display style to none. The media queries are hidden from you in the breakpoint system.
Or, conversely, you could hide it at desktop, and then choose a smaller ( e.g. tablet ) and/or larger ( e.g. 1280 ) breakpoint to make it display: block at.
All styles are defined at the desktop breakpoint and the rules propagate outwards. You’ll need to dig into Webflow U if this isn’t familiar to you yet, it’s very fundamental to Webflow design.
You can share your published site link with details on where to find the IFRAME in the page if you like. If you’re having troubles with display: none directly on the Embed, you can wrap the embed in an additional div and hide that instead.
There’s nothing weird about your IFRAME and it could not override your parent document HTML. Script-generated popups might be possible(?) from a hidden IFRAME.