Use a separate computer 100% offline (not before, not now, not after), wipe it before first use and install an os with the help of a usb key generated with the proper tools.

Use the genuine command line tools to generate your keys on it, there are also tools to sign a transaction offline on that same computer, use the generated tx json file, which won’t contain any useable key but a signed transaction, on an online computer to send it with another command line, use it for testing the generated address.

I used a broken laptop 9 years ago and it still holds my very first BTC.

You can store your crypto on a hardware wallet like ledger. Thats the most secure way as it requires input from your hardware every time you make a transaction. You can also scan your system with malwarebytes to check for malware.

I would like to know the same… I’m 99.9% sure malware isn’t an issue when it comes to a cold wallet. It would still be nice to know how to check and clean iPhone/Computer from malware though as preventative.