Reading with O₂ connected doesn't mean anything. You will probably get some resistance value but it's though the DME not helpful.

If you found any that read not OL that's the job you were tasked to perform.

It sounded like it would be an upstream sensor maybe melted to exhaust manifold. You are very close to solution.

__________________
2011 E70 • N55 (me)
2012 E70 • N63 (wife)