Generic repository in ASP.NET Core without having a separate AddScoped line per table in Startup.cs?

Just use the non-generic registration overloads (the ones where you need to pass the 2 Type objects.) Then provide the open generic types of both your interface and the implementation:

services.AddScoped(typeof(IGenericRepository<>), typeof(GenericRepository<>));

In your controller, add a dependency for a repository of a specific type (a closed generic type):

public HomeController(IGenericRepository<Lookup1> repository)
{
    ...
}

If you would like to register all IGenericRepository<> implementations in Assembly:

services.AddAllGenericTypes(typeof(IGenericRepository<>), new[] {typeof(MyDbContext).GetTypeInfo().Assembly});

With extension from: https://gist.github.com/GetoXs/5caf0d8cfe6faa8a855c3ccef7c5a541