Remove everything after the closing parenthesis

[ohrenkino]

See the documentation:

Regular Expressions – Mp3tag Documentation

and all in all it takes any number or any character until a square bracket appears and stores it in $1 and then it addresses everything following the square bracket. And then it returns the value stored in $1.

See also here for other solutions:

Remove everything from first parenthese going forward

how do I create an action that will remove everything from the first parentheses going forward. ie. track name: Molly (ULTI-reMIX by Mark Roberts). I want to remove "(ULTI-reMIX by Mark Roberts)"