I meant that he should NOT keep private key backuo in .txt file or any other digital file format.
People tend to to this sometimes, instead of writing seed words on paper.
But this wouldn't be too much of an issue either.
If the computer is air-gapped and the hard drive is encrypted, storing the seed on the hard drive would not decrease the security at all.
I agree that a digital backup should never be the only backup (in case of electronic devices breaking).
But the digital backup itself should no be a problem at all.
If the computer is turned off, no information can be extracted (encrypted hard drive).
If the computer is turned on, information can be extracted from the backup file AND the wallet (so no difference either).
As long as the computer is air-gapped and the harddrive is encrypted, that would be fine.
Or which situation can you think of where the digital backup would reveal the seed while the wallet file wouldn't ? ?
So you say it is OK to create digital files backups on computers, and you are willing to take that risk?
If operating system is Windows, it is not so hard for hackers to bypass or crack login,
and I am not sure most people password protect files (like I do) or encrypt hard drives.
If hacker steals your computer, knowing that you have bitcoin wallet in there, he will do everything to extract information he needs.