What is it you are looking to do in post?
- You do mean Render Elements, not passes?
- You do mean LightSelect render elements (as multiple LightMix passes won't do anything at the moment)
- Save All from the VFB will save all render elements separately, including LightSelects (but also any other render element too), to whatever file format you pick
- Saving to CXR will give you a file you can edit in the Corona Image Editor, and that CXR will contain all the LightSelect passes