I tried both ZGC and Shenandoah (with plenty of heap space available) and haven't noticed much difference compared to the default CMS. Also, Shenandoah (or maybe both?) does not support compressed pointers, so there was a noticeable increase in memory usage.

Personally, my experience with jetbrains IDEs is not that they lagged, but simply that they were slow.

ZGC would probably harm more than help.