I am getting the following on the Blender (4.2.3 LTS) console upon start-up:

Error in bpy.app.handlers.load_post[1]:
Traceback (most recent call last):
File "...\AppData\Roaming\Blender Foundation\Blender\4.2\scripts\addons\io_scene_valvesource\utils.py", line 171, in _onLoad
State.update_scene()
File "...\AppData\Roaming\Blender Foundation\Blender\4.2\scripts\addons\io_scene_valvesource\utils.py", line 159, in update_scene
make_export_list(scene)
File "...\AppData\Roaming\Blender Foundation\Blender\4.2\scripts\addons\io_scene_valvesource\utils.py", line 527, in make_export_list
scene.vs.export_list.clear()
^^^^^^^^
AttributeError: 'Scene' object has no attribute 'vs'

Haven't tried to actually use the tools to import/export.