if you’re going the mail merge route, you should be able to do something similar to what’s described here: https://forum.inaturalist.org/t/using-microsoft-words-mail-merge-to-display-images-from-exported-csv-list-of-observations-that-includes-image-urls/36591.
that tutorial describes how to display actual images based on an image URL, but you could also apply this concept to display a QR code image generated dynamically via an API like https://goqr.me/api/. for example, here’s a request URL that should return a 150 x 150 px QR code image for the observation 137315826: https://api.qrserver.com/v1/create-qr-code/?size=150x150&data=https://www.inaturalist.org/observations/137315826.
so if you follow the tutorial instructions, substituting the image URL for an appropriate QR code image URL, i think you should be able to get what you’re looking for.