They really need to update the default memory footprint. The 750MB default isn't enough for any projects these days and they don't exactly make it obvious how to update it to 2-4GB.
No need as you’ll get a warning on low memory if you’re on a large project, and IDE will advice you to increase heap size (just click provided option) and you can manually choose how much memory to provide.
In my experience, IDEA becomes GC bound quite readily during indexing which in combination with indexing blocking most operations stalls the UI.
It's not that the IDE OOMs, it's that it burns cpu cleaning up objects in stop the world collections. These stop the world events can be mitigated with additional memory.
So it’s fine that default is relatively low.