There has been quite a few posts regarding Lemmy apps for iOS, and their installation process might not be straightforward since they're PWA or beta. Here's a list of apps mentioned and their links:
⭐ Released
Voyager (formerly wefwef) (📱PWA)
To install, open link in browser and follow instructions
Works well enough. Pretty much a wider version of the app (I use my iPad in landscape) so it's not using the space optimally, but I can't fault the apps especially since they're all new and focused on iPhones first.