If you need to add any custom code in between any elements in your โ๏ธ Email frame, such as platform specific template/conditional tags, you can insert a ๐งโ๐ป Custom Code layer to do this. It will be added as a Figma text layer, which you can paste your custom code into, and have that rendered out as plain code when the email gets exported to HTML.
๐งโ๐ป Custom Code layers can only be added directly to an โ๏ธ Email frame as a way to inject custom code blocks between ๐ฃ Content Row, ๐ฆธ Hero and ๐ Row Wrapper layers in your email design.