Electrum is not a cold wallet unless you use it on an airgapped device.
The wallet that I have used for altcoins which is open source is Unstoppable. You can use it on an airgapped device and have its watch-only wallet on an online device for transactions. The problem is that it is not supporting some altcoins.
Or you can buy a hardware wallet like Trezor.
I would highly appreciate if you're going to drop the link here for the "unstoppable" wallet and where can I buy a legit trezor wallet. I'm planning to diversify my portfolio since it's still a good time to bag some alts.
My first thought was I'm gonna hodl it on a certain exchange but it's still better if I hodl my own keys for better assurance, can't risk it nowadays, especially the SEC here in our country is very shitty.