, you can use electrum cold storage wallet, and generate your keys on an air gapped device.
Is this a physical device like a usb?
No it is not. You can use an old PC or an old phone to set up your cold storage wallet, but after you must have downloaded the app from electrum website. You disable your internet, before generating your keys, and you will never connect that wallet to the internet again.
You will create a watch only wallet that you can use to monitor, sign, and broadcast transactions.
https://electrum.readthedocs.io/en/latest/coldstorage.html