If you have a nonstandard unicode character in your password and an attacker tries to crack a password based on the assumption that no nonstandard unicode character is in the password, they can’t crack your password no matter how much compute they throw at it.
Given that you decide where in your string you place it, the attacker would have to test for the special character being at multiple different positions which adds a lot of additional entropy.
If you have a nonstandard unicode character in your password and an attacker tries to crack a password based on the assumption that no nonstandard unicode character is in the password, they can’t crack your password no matter how much compute they throw at it.
Given that you decide where in your string you place it, the attacker would have to test for the special character being at multiple different positions which adds a lot of additional entropy.