Fully boxed text fields vs lines

I'm wondering if there is any evidence-based research or studies on fully boxed text fields vs lines? It seems that using lines is the current trend, for example, Gmail, Invision, and even some desktop software such as Adobe XD. My initial reaction is that it seems it could reduce cognitive overload - so less visual information for the brain to process. But what about the downsides?

But some apps are still using the fully boxed fields such as Asana or Sketch.