Copy prototype link and open in chrome, if you work in chrome already just view prototype.
Go to chrome web store search and install the Awesome Screenshot extension.
Open prototype page, hide figma UI cmd+\ click the extension icon to open it’s window, with the ‘capture’ tab selected and select ‘full page’ don’t mvoe your mouse or keyboard until the new tab opens with the full screenshot, the extension will automatically scroll the page and stitch the screenshots together giving you a complete full page preview.
You can download the link or link from the shared link in the extension.