You must reference Oracle Data Provider for .NET (ODP.NET) version 23 in your Visual Studio project. You can do this by using the Nuget Package Manager and searching for and including Oracle.ManagedDataAccess version 23.

Any other version of ODP.NET will result in the Entity Framework Designer crashing or throwing errors.

If you must use older versions of ODP.NET, then you will also need to use older versions of Oracle Developer Tools for Visual Studio. The major version of Oracle Developer Tools for Visual Studio must match the major version of the Oracle Data Provider for .NET referenced by your project.