You can reset the password in Mojave by entering recovery mode and using the "resetpassword" utility via the terminal:

1. Boot your Mac while holding CommandR. When you get the Apple logo release the keys and allow the Mac to come up in Recovery Mode.
2. When you get to the macOS Utilities dialog select Terminal from the Utilities menu
3. Type resetpassword into the terminal window. In a few seconds the reset password utility will open and allow you to reset the password on your account.

Once you mount the file system, you should be able to use passwd username and then put in the password twice.

The drive is locked using FileVault encryption and cannot be accessed until you unlock the drive. This may be set to a master password of yours, and often is set a while back. You may want to try older passwords (or versions of them) to see if any of those work.

To unlock the drive:

1. Boot into the recovery mode
2. Launch Disk Utility
3. Select the drive in disk utility
4. Click unlock near the top of the disk utility window

Unfortunately, the drive will not allow you to boot into those options and/or work on it until you pass the encryption lock. It will require a password or for you to completely erase the drive.

This answer assumes you have the login and password for an admin account within Ventura (possibly earlier version but I have not tested these).

1. Login on the Mac as an admin user. Let us assume this user is called admin

2. Now open Terminal.

3. At the command line, type:

   dsenableroot -d

4. You will see:

   username = admin

   user password:

5. Type the password for the admin user. You will see:

   dsenableroot:: ***Successfully disabled root user.

6. Type

   dsenableroot

7. You will see:

   username = admin

   user password:

8. Type in the admin user password again. You will see:

   root password:

9. Type in your new root password (twice)

10. You will see:

    dsenableroot:: ***Successfully enabled root user.

Finally, don't forget your new password.

There are at least three ways to reset the login password of an account.

Using Reset Password.app on the recovery partition:

1. Hold command-R on startup.
2. Select Utilities > Terminal.
3. Run resetpassword, which opens the Reset Password application.
4. Select the volume and account and reset the password.

Using dscl in single user mode:

1. Hold command-S on startup.
2. Run mount -uw /.
3. Run launchctl load /System/Library/LaunchDaemons/com.apple.opendirectoryd.plist in 10.7 or later or launchctl load /System/Library/LaunchDaemons/com.apple.DirectoryServices.plist in 10.6 or earlier.
4. Run dscl . passwd /Users/username password where username is the name of the account and password is the new password.
5. Run reboot.

Creating a new admin account:

1. Hold command-S on startup.
2. Run mount -uw /.
3. Run rm /var/db/.AppleSetupDone.
4. Run reboot.
5. Go through the steps of creating a new account.
6. Reset the password of the old account from the Users & Groups preference pane.

If FileVault 2 is enabled, you need to enter a password to start up in single user mode, and the list of accounts in Reset Password.app will be empty, so none of these methods can be used.

None of the methods above resets the password of the login keychain. If automatic login is enabled, you can print the password of the login keychain by running a command like this in single user mode before resetting the login password:

sudo ruby -e 'key=[125,137,82,35,210,188,221,234,163,185,31];IO.read("/etc/kcpassword").bytes.each_with_index{|b,i|break if key.include?(b);print [b^key[i%key.size]].pack("U*")}'