@cinziaisabelferrari re the first question, it depends on how Wix does it under the hood (as I said earlier, I don’t think you should go in this direction).
Re iframe/custom element see:
https://support.wix.com/en/article/velo-working-with-the-html-iframe-element
https://www.wix.com/velo/reference/$w/htmlcomponent
https://support.wix.com/en/article/wix-editor-adding-a-custom-element-to-your-site