Unable to create a constant value of type ‘’. Only primitive types or enumeration types are supported in this context.

the problem appears because you are using contains method in non primitive type
here is an example

Audit audit = new Audit();
List<int> ints = userReports.Select(y => y.ReportId).ToList();

List<ReportUserVisit> userReportLastMonthVisit = audit.GetAudit(userId, AuditType.Report)
                .Where(x => ints.Contains((int)x.ObjectId))
                .Select(x=> x.ObjectId)
                .GroupBy(x=>x.Value)
                .Select(x=>new ReportUserVisit { ReportId = x.Key, LastMonthVisitCount= x.Count() })
                .ToList();

note ints object, this will solve the problem.
because ints collection is list of int it can use contains method inside entity framework