Issue  posted in the Google Sites Help Community:
https://support.google.com/sites/thread/257606157
Quote: User 5724919240798171380
I've embedded a couple of google docs in my site; both have hyperlinks (...). Links work fine on my computer, but on my phone these links open the document in Google Drive, not the target pages. Some page visitors report the same thing on their computers. Dox are set to public (anyone with link can view). Please help...what am I missing?
https://docs.google.com/document/d/1W_4MxXb8MzVymsA9uL03BLl7-980TM6OwFwbfoKrMeE/edit?usp=sharing
⚠ On the phone this method does not work as intended. You can't click the link directly, the document will open in the Google Docs viewer, where you can then click the link (while using a Google Sites URL).
If you use a custom domain name the browser additionally asks you before opening the Google Docs viewer. There are some differences between the browser messages you get whether you are using Chrome or Firefox (which I have tested) and whether you are logged in to a Google account or browsing in an incognito window.
You can alternatively publish the doc to the web (Docs Editor Menu > File > Share > Publish to web) and use the 'pub' HTML version of that document. The links are directly clickable.