Cannot unlock Users & Groups settings
Solution 1:
You're best bet is probably to just boot into macOS Recovery mode and then use the resetpassword command in Terminal to reset your password.
More specifically:
- Power off your Mac
- Boot into Recovery Mode by holding down the CommandR keys while powering up your Mac
- If prompted, select your language and press enter
- Go to Utilities > Terminal.
- Enter
resetpassword(all one word, lowercase letters) - Press Return
- Select the drive with your account (typically the main drive)
- Choose your account using Select the User Account.
- Enter a new password
- Re-enter the same password
- Enter a password hint
- Click Save
- Ignore the warning about the password changing
- Click OK.
- Shutdown your Mac by going to Apple > Shut Down
- Restart your Mac normally and use the new password to log into your account
- Once logged in, test to see whether you can unlock the Users & Groups preferences pane
Next steps
If you still can't unlock the Users & Groups preferences pane after the above steps, it may well be that you have no Admin account on your Mac. If so, refer to the following for further info:
- I don't have administrator account on my mac
- From Standard to Administrator