Is it safe way to use sign in for user's convenience?

I’ve been not so active these days, but actually, I was trying to make a new game app. To do it, I needed to provide the sign in to use firebase. For users’ convenience, I’ve fixed some things from basic code. This code saves the email and password to local storage and signs in automatically. If it causes an error, you will have to enter email and password at SignUpScreen. Will it be safe?

If not, please provide some ways to make it safer.

The general rule when saving passwords - always store them in encrypted form, for example, using md5 encryption. If the attacker can obtain the data with the password, he will see the encrypted data. If data is stored without encryption, he will immediately see the passwords.

Unfortunately, in Thunkable X no encryption. Local storage is not intended for storage of secret data.

Then, users might feel uncomfortable about typing the email address and password, so what if I just remove the sign in? I don’t think there will be any problem because I will use realtime DB only for online battle, which doesn’t include password or important information about the user. (And it will be deleted as long as the battle ends. Also, the user data will be saved in local storage.)