Tattoo, engraving on the walls of caves, etc. Just don't think too much about it. How many backups do the banks have of account information? 2 or 3, so for bitcoin that's enough.
The problem of banks they're store every accounts information in online, so they can access it whenever they forgot or the data are corrupted in offline storage. Even the hacker know anything about the user's information, they can't have access with the funds or they could freeze your funds if you withdraw large amount money due to suspicious activity.
In non custodial wallet, no one will control the user, that's why store private keys or seed phrase in online is really a bad idea.
Honestly having a backup in physical are work same, the only thing is different is the media/tool you used.