Forgot password for system preferences

When you install any macOS update, you are required to enter a password,

That is the administrator password.

If you forgot the Administrator/ login password

https://support.apple.com/en-us/HT202860

Websites password.

Launch Safari.

Safari > Preferences > Passwords

Enter your account password.

Password pane will open.

Highlight / select an website entry. Password will be revealed.

The first account you created on your Mac is by default, an administrator account. You'll need its login password in order to make changes to your Mac.

Just out of curiosity, does your Mac ask you for a password when you wake it up? Do any other user accounts exist on your Mac? If so, are any of them administrator accounts?

Forgot administrator login password?