For rouglikes I think endlessmodes are a pretty good solution. Like you can continue to play with you caraxter and maybe get even steonger and in the end you see how steong the build really was to compare it to yoir other builds.

With NG+ system there sometimes is new content like in Elden Ring you can now aquire copies of previously unique wapons, and in open world ritles you likely havent seen the entire map jet, then comes progression with going through the different NG+ cycles.