Hello @RomeoArabov
I’m not sure, because I can’t login to the site (they are not hosted by us afaik), but it could be that they are using a smaller than usual font-size, which will force a zoom-in specifically on Safari.
It is odd that normal browser-safari works for you though, but it still very much sounds like that issue.
When you say Discourse app, do you mean the Hub, downloaded from the App Store, or the PWA?