This is an interesting question that hasn’t really be solved yet properly - or more like I haven’t found a real answer yet.
Most of the answers mention the engine scalability settings but those only govern the play mode.
At the same time, the editor did lower my resolution etc. brutally when it realized the rig I was using was way too weak - this affected both the play mode AND the preview which you see during editing.
Sadly it didn’t do that ever again so now, at the same weaker rig, I can’t manually reproduce that lovely low-res preview.
It’s really weird. Maybe I can try setting graphics in world construction blueprint or similar? 