The "Insert Render Frame" has been around for awhile and I don't believe it makes a very nice final file. Even at 300dpi and viewing with Acrobat the image is blurry. It's like making a PDF from a gif or other lossy format. It doesn't produces a true vector output that's scalable to any size like with a Latex document made from a dedicated Latex compiler.
I believe the "Math button" feature is supposed to work by rendering the Latex in eps , SVG or other scalable format then insert it into the Scribus document, then finally export the whole document to PDF. I could do this manually but it would be very tedious for large documents.