If you search for "remove part of title" you get a lot of already existing answers for your question.
Which ones have you tried already? What exactly doesn't work for which expression?
One of the working expressions could be: $regexp(%TITLE%, \(.*\)$,)
This would search for a space, an opening bracket, any character until a closing bracket - and this has to be at the end - to leave brackets and text between brackets before the end untouched, like "My (super) text and other blabla"
I've found a suggestion by Florian about my problem:
Guess value
Source: %title%
Format string: %title% (%dummy%)
It works fine, but I should now better specify my requirements.
Some titles sound like "Chasing pavements (Live) (xyzw 1)" or "Tango guapo (20sec. ouverture) (abcd 1)" and I would like to remove only the last suffix, i.e. after the adjustment the titles should be "Chasing pavements (Live)" or "Tango guapo (20sec. ouverture)".