I tried to install the android version and during the setup it only allow to create a seed phrase with 12 words. Is it possible to use a 24 words seed phrase insteed?
Electrum wallet is 12 word seed phrase by default and you are not the one to create your seed phrase but electrum does that for you. Since you said it's Andriod version, it means that you should just copy your 12 seed phrase and back it up because it's very safe since itvhas 128bit entropy which is secured enough.