Older Tomodachi Life games, especially the 3DS-era entries, really did use Mii QR codes a lot for sharing characters. That is why you can still find old QR images, character QR collections, and old tutorials online.
But the new Switch game, Living the Dream, is not the same system as the old 3DS version, so it cannot scan and use those original QR codes. Treat the old QR code as a design reference instead. You will need to copy and rebuild the Mii manually in your own game.
This site is curated by hand to collect designs that are actually convenient to recreate, with clear pictures and useful instructions. In most cases, that means easy-to-read grid references, not old QR codes.