I have verified that this extension works correctly with GDevelop 5.0.130.
The version of Tiled I was using was 1.7.2. I have upgraded Tiled and verified that it works correctly with 1.8.2.
Unfortunately, I have no plans to add the ability to generate collisions from multiple layers at this time.
However, if many users request it, we will consider it. Please post here if you would like to have this feature.