I'm not really sure what's happening. I cloned a Gitlab repository and when I see the folders/submodules in the command line it matches what is on my remote repo.
Remote Gitlab going into model_target folder, it has csar_lib:

Git on command line, in model_target folder:
But when using Git Extensions, model_target folder:

It's showing csar_utilities instead of csar_lib.
They're all pointing at the same commit ID, that's why it's a bit strange to see the difference.

That should mean in command line, you use a
git clone -recurse-submodule, which cloned the parent repository and its submodule.But the Submodule view of Git Extension only lists submodules root tree.
The latest Git Extension release 4.0.0 does include a PR 10145: Open new instance if double click on current submodule: