The approach
Not a migration. A selection.
There is no import. That sounds like a limitation and is mostly a filter: typing a secret in by hand forces you to decide whether it is worth the minute.
Start from your existing store, the password manager, the notebook, the envelope, the photo you have been meaning to delete. Read down the list and mark only what you would still be upset about in a year.
Most people end with somewhere between five and fifteen items. That is the vault. Everything else stays where it was, which is fine.
One evening
In order.
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I
Gather
Put every place you keep secrets in front of you. Include the ones you are slightly embarrassed by.
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II
Choose the password
Decide the one you will remember before you type anything else, and rehearse it a few times.
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III
Write the vault
Name each secret plainly, Banking, Wallet backup, Home safe, and enter its value. Then encrypt and write to a card.
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IV
Copy to three
Write the same vault to each card, and put each one where it belongs.
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V
Clean up
Delete the screenshot. Shred the paper. Empty the notes app. That step is the actual improvement.
Fifteen secrets,
one evening, three cards.