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)
{
    ...
}