How can I implement a global exception handler in ASP.NET Core to catch unhandled exceptions?

In ASP.NET Core, you define a global exception handler using middleware. You create a `Middleware` class that implements the `IRequestPipelineMessageHandler` interface. Within the `OnHandleRequest` method, you catch exceptions and log them. You can then return an appropriate error response, such as an error page or a JSON error message. The middleware is configured in `Startup.cs` or `Program.cs`.