While we don't currently support embedding iFrames in Tettra, this is something we're considering for future product work. If this is a feature you'd be interested in, please reach out to Support and we'd be happy to keep you posted!
In the meantime, we have quite a few built-in integrations with many of the tools our users like to reference in Tettra. For more information on available integrations for embedded content, check out this article.