As far as i know Unstoppable Wallet is open source. How would it compare to an open source cold wallet like for example Onekey Classic?
The hardware wallet is always better than any hot wallet like Unstoppable. Although Unstoppable Wallet is a recommended wallet for storing your coins and it is open source too but this does not mean that it can replace the hardware or cold storage wallet.
I haven't use Onekey Classic but I would have never used it only because it has vulnerabilities in the past, although fixed, but why i should be buying a wallet with past vulnerabilities?
I know hot wallet, cold wallet. But...in case i would use the hot wallet on an iPhone that has installed only the wallet and have internet connection...would it be possible to get hacked in a way if only that would be the use for it?
Any wallet which is installed having an internet connection means it can be hacked. You may make an air-gapped Bitcoin wallet on the iPhone that never touched the internet. It can act as a cold storage and believe me it is better than to use Onekey Classic, which has doubts in mind about past vulnerabilities.