I have every robot body except for the bottom two corners. They are all upgraded. Boss C wipes the floor with me. Is there anything I can do or is the game dead to me?

Question to anyone who may have completed the game thus far. I have beaten all of the bosses on my live stream the other day, but I cannot locate the next step. I am sitting on 96% map completion, but can't seem to find anywhere else to go with no real indicator as to what my next step is. Is my game bugged? Or did I miss something?...

The long vertical hall on the upper left of the map looks like it should be surmountable by the flame wheel mech, though the last boost always seems to kill your momentum and I otherwise cannot get three screens up. Is there some other route here?

up / down works, but can't select anything...

The game doesn't seem to sync saves to steam and I can't locate the save-data. Anyone know where to look?