That sprite overlayed over the screen to simulate a flashlight is probably the simplest way.
With the C3 engine we are pretty limited with what we can do with 3d lighting.
Hard shadows can be possible as shown by this test. But it may not scale well with more objects.
construct.net/en/forum/construct-3/general-discussion-7/possible-add-3d-light-172761
Even with JavaScript there isn’t much you can do to make 3d lighting with c3’s renderer. What was done with most of the 3d stuff in C2 is another engine and renderer separate from construct was stacked on top or underneath your game. That’s what q3d did. Another option was to use constructs renderer in a way it wasn’t intended to be more integrated with the game. Rojo3d did that in c2. In c3 that is much harder, and even if a way is found to do it c3 is constantly getting updates which would require constant updates to keep the solution working.