Yes, IP address measures are an absolute waste of time and effort.

There are other technical proposed methods to ban an individual from a forum, but each of them have major flaws making them not viable.

Arguably the best way to "ban" someone is to "shadow ban" them. This entails the forum admin configuring their forum in such a way that all posts made by the troll user are visible only to that user and nobody else, if they have the technical capability from a software perspective to do it.

This should at least provide for a period of peace on the forum, until the troll user realises that they've been shadow banned. Then the whole cycle of identifying the next fake user and shadow banning that one starts again.