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Factory reset and later disconnect your phone from the internet, then setup encryption and use it only to store secure passwords like recovery keys or Bitcoin private keys... It's like a cold storage in a safe, but cheaper, more convenient, and possibly harder to steal.
One of the most secure setups is running KeePass2Android Offline in an Android device that remains in flight mode, flashed with CopperheadOS.
Specs
Pros
Pro Similar or better security than a cold storage
Similar to some physical password vaults, like Password Vault by Hammacher Schlemmer, it's safer than most cold storages because if someone gets your device it's harder to brute force both encryptions than opening most vaults. Also you likely have time to revoke all existing tokens/passwords before the attacker.
Pro Safe against almost any attack vector
Storing for example OTP back-up codes in a password manager connected to the internet (your home computer, LastPass, 1Password...) is somewhat secure but you always risk that a software exploit may give an attacker access to your accounts/data. An offline storage, however, may not be compromised as there is no attack surface. You only risk something if someone grabbed your device, but even then you are likely capable of revoking any password/token stored on that device very quickly.
Cons
Con Only for rarely accessed passwords/data
You cannot copy/paste or fill forms that way (as the device is offline). So it's not viable to store commonly used passwords. It's only good to store rarely used critical data, like: OTP back-up codes, cryptocurrencies, recovery keys and such.