The Gurobi ObjBound attribute applies to MIP models only: https://www.gurobi.com/documentation/9.0/refman/objbound.html. I’d recommend going through the Gurobi documentation or asking Gurobi support to figure out the attribute that you want to query, then follow these instructions to query it from JuMP. JuMP can return only the information that the solver itself exposes.
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