Remove old ceiling pancake (pan) junction box, or how to work around bolt in that box?
You don't need that bracket

The bracket you depict in your photos is intended to provide a mounting stud if your box lacks one.  Since your box has a stud already, the thing you need isn't that bracket, but a piece called a hickey that screws onto the existing mounting stud and then provides a place for the fixture nipple to screw into, allowing the wires to exit it:



Oh, and make sure to put that nut back on the fixture stud, by the way, so the box doesn't wind up putting excessive stress on the conduits in the ceiling.