It's caused by mycrypto gives me more ability to create a wallet even when i were in offline mode.
Not saying you should use it, but you can also use MEW offline. Read more
here. I think MEW and MyCrypto are more or less at the same grade. Not the best choice if you're looking for long-term storage and security.
There are so many ways that already offered to sign in your wallet but the most popular one must be through the private keys. It's caused by you didn't need password but this less secure compared with keystore.
You should look for alternatives since inputting private keys or uploading keystore is prone to a phishing attack. Using an open-source hot wallet should be a bit better. You can also try using a hardware wallet/cold-gapped device for long term purpose. It might cost you some money, but it is worth the money as long as you choose the right one. Avoid closed-source or centralized wallet even if they claimed that they open source some of their apps.
OP, if you created a wallet through the MEW website through software methods, so keep the Keystore file on an external hard drive, and never forget the password that you entered after creating the wallet.
Make sure to never store it on cloud too. Some people lose money because they store their file on cloud (things like Drive, or even Telegram saved messages). It is better if OP move from a risky tools like keystore in the first place, especially if they are newbies and can't prepare the appropriate security measures to protect their wallet.