This typically only happens when you make changes to your system user name/password credentials. Typically, only a user with the same logon credential as the user who encrypted the data can decrypt the data.
If that information is gone, then the “key” to the encryption is gone. But you’re not saying you changed devices or anything like that on your device, are you?
Do you only have Brave on one device? In other words, have you ever done Sync between devices? If so, might just be easier for you to add your desktop to Sync with other device that has your updated passwords. You’d then have access to it all.