I’ve looked into it before, and Apple developer accounts cost $100 every year, which I am not willing to pay out of pocket. If someone decided they wanted to donate that amount every year, then I would probably reconsider. I also don’t have any Apple hardware, so I would need additional help in that regard; I could emulate macOS (which is a pain though), but I would need someone to actually test on a real iPhone.
Not sure I understand your question, but Interstellar is built with Flutter, and currently supports Android and Linux (x86_64) via Google Play, F-Droid, and Flathub. And yes, it’s both Lemmy and Mbin.