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
I am going to give wefwef a try. I was using Mlem at first but I wasn't a fan. Still a bit worried about wefwef as I wasn't a fan of Apollo at all but willing to try!
Unfortunately most of these are Apollo clones since it was very popular. I'd suggest Liftoff if you prefer a different thing. It uses a different design but still nice. Although I haven't tried Thunder so I'm not sure about that one.