Nobody wants to be deceived, but some people choose to deceive themselves. If you warned him that it's unwise to store that type of backup in the cloud and he chose not to believe you and to go another way, that's his problem...
I keep my backups locally. I once made the mistake of saving to Google Drive, but I quickly realized it was a bad idea. Fortunately, nothing serious happened to me, like my information being stolen, but what I see daily is services like that being compromised by password theft. The problem is that, nowadays, everything is in the cloud; companies practically manage their information and that of their clients in services like Google Workspace. So, in a way, everyone is doing it wrong!
I think other information being kept in clouds is not a problem, because clouds are generally a good way to keep your data and stuff because you can easily access them from anywhere and with any device as long as you can log into your account.
However, when it comes to sensitive information such as your wallet details like seed phrase or private keys, your bank account information that you can use to log in, or anything else that is related to finances and your financial holdings that can potential put your assets under risk should not be kept in online clouds because even if the company itself is trusted and trustworthy, your account could get compromised and then it can become a problem for you.
Even when you are doing it locally, like saving it in your phone or somewhere, that can also be risky because devices are also getting compromised these days through malware and other ways scammers are using to gain access to people's devices. So it's probably better if we keep these things out of the devices we use or the online clouds and stuff, we should write them and keep them physically somewhere where we know they won't be accessed by anyone else other than us, and we should try keeping multiple copies at different places if possible, for better safety.
