I feel paranoid.
Paranoia can cloud your judgment. It's good to be cautious, though.
What will be your suggestions?
There is no direct threat to your Ledger Nano S at this time. Nevertheless, if you feel uneasy or don't feel safe with your current storage solution, it's always a good idea to explore other options.
According to what I read, you are safe if you do not update the firmware, but after several months you will reach a point where you have to update the firmware, and then you can fear, until that thing happens, start thinking about a suitable alternative instead of worrying.
If he keeps using the Ledger Nano with Electrum software, he won't need to upgrade the firmware unless he chooses to do so. Firmware updates are exclusively carried out via Ledger Live.