This is to be expected, as MS Oracle is the System.Data.Oracle ADO.NET provider which isn't supported on .NET Standard, but is on .NET Framework. So you shouldn't choose .NET Standard as target platform, but .NET 4.5.2 or higher.
So the code generates for .net standard, but the DQE isn't available on .NET standard. If you're planning to use the generated code on .NET Core, please switch to the ODP.NET provider. This isn't a simple switch, as MS Oracle has the side effect that all NUMBER(x, y) types are System.Decimal, so you have to refetch the relational model data using ODP.NET. ODP.NET is supported on .NET core and therefore is supported on .NET Standard.
If you're planning to use the generated code on .NET Framework, then please select the .NET framework of choice, e.g. .NET 4.5.2.
Please explain what you're planning to do: use it on .net core or use it on .net framework so we can advice you what to do next.
(In general you shouldn't pick MS Oracle as your ADO.NET provider for Oracle as Microsoft has deprecated System.Data.Oracle several years ago and doesn't add new features to it. Instead use the latest ODP.NET managed provider from Oracle itself)