I have gone beyond step 85 but the yellow assembly installed then is still loose, not connected to anything and can be pulled out. I want to make sure this is right as I do not want to go much further and find I have to disassemble and go back. Does it connect later?
I haven't assembled this model, so my answer is based on online building instructions.
Now if we go back to Step 82 we can see what's is going on behind assembly seen in Step 85. Here, I've marked same points that would be visible behind Light Bluish Gray 13L beam. So assembly in Step 85 goes into "7" connection point and would be inserted into one of two Yellow 2L Technic connectors.