forgot password for time machine

From this article: About the Time Machine backup password on Mac - Apple Support

About the Time Machine backup password on Mac

To encrypt the Time Machine backup, you must provide a backup password. No one but you should have access to your password. Choose a hint that helps you remember your password. To restore files from encrypted Time Machine backups, you must provide your backup password.

Important: If you lose or forget your password, you will not be able to restore or recover your data.

If you’re using macOS and Time Machine with your Time Capsule as is typical, the passwords for the Time Capsule device and for the remote storage access should be available in your system keychain. Open Keychain Access.app, and search for the name of the Time Capsule. The Keychain record types will show which password is which.You’ll have to authenticate with an admin user to gain access, but the password is available as,Time Machine needs it.

That is pretty basically correct.