There's Unstoppable wallet which is open source, I have tried the Android version but never the iOS one:
https://unstoppable.money/Unstoppable wallet should just be for altcoins, it is not having many other features that reputed open source wallet have. It deos not have RBF and coin control. Bluewallet is still the bet choice for iOS.
Apart from Bluewallet which I believe is an open source bitcoin wallet on iOS, there is Bither, BitPay Wallet and Edge Wallet. Edge also supports other crypto assets besides bitcoin
This wallets do not have some of the features that Bluewallet has. I can not even recommend these wallets. Almost all bitcoin wallets that have excellent features are not supporting altcoins.