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Android and iOS EX actually both use the rust SDK under the hood, but iOS is usually used as the test bed so it gets features a little faster than Android. EX iOS just got a stable version of it a couple days ago, so a more native feeling login process for SSS on Android should be coming very soon!
You might try a Matrix group instead. Doesn’t require a phone number and supports more than 1000 users unlike Signal. Search is bad though unfortunately.