Creating cold storage using Electrum is not secure as hardware wallet since you're still connecting to internet to download Electrum or you're connect it with your insecure device. The device either Android and IOS aren't secure too since we don't know what's the other applications will do, you can't delete all of the applications that installed on your device. The @OP himself is care with his privacy, using Electrum that connecting to centralized server will leak your privacy, you must need to run full node.

The safest and secure way to create cold storage is this tutorial, but it's really complicated to done [Guide] Secure air-gapped crypto wallet storage method.