Write it down on paper, put it in an envelope, and leave it in your home, preferably in a small fire resistant lockbox that you keep other important documents in.
If your home isn't secure enough for this purpose due to roommates or other issues, ask a trusted friend, parent or relative to hold onto it and your other important documents on your behalf. If your situation makes putting it in someone else's hands a problem, you can split the password or other key material between multiple locations as well. 1Password makes it easy with the "rescue kit", and KeepassXC can use a combination of a password and file-based key for this purpose.
Security conversations on this topic typically go down some rabbit hole about the government, police etc. Keep it simple and don't crawl into that hole. End of the day, in the United States, the most reliable and legally secure place is your home or in some cases an attorney's office.
Safe deposit boxes are an option but are expensive, inconvenient and often less secure. A bank clerical error, fubar, or payment issue could result in loss of the contents at any time. (See: https://sacramento.cbslocal.com/2018/07/26/safe-boxes-stolen... )
When you need your password at 4:30PM, the bank is closed.
Also, it’s an awful place for important documents like a will, as the bank will require a court order for your family to open it upon your death.
If your home isn't secure enough for this purpose due to roommates or other issues, ask a trusted friend, parent or relative to hold onto it and your other important documents on your behalf. If your situation makes putting it in someone else's hands a problem, you can split the password or other key material between multiple locations as well. 1Password makes it easy with the "rescue kit", and KeepassXC can use a combination of a password and file-based key for this purpose.
Security conversations on this topic typically go down some rabbit hole about the government, police etc. Keep it simple and don't crawl into that hole. End of the day, in the United States, the most reliable and legally secure place is your home or in some cases an attorney's office.