[Solved]-nested select projection with index in linq using EF Core-LINQ,C#

Apparently the question has been answered before, because of the new framework, the error message is different, and because of how I got to the answer, thinking that projections where interfering with how the indexer was working.

LINQ to Entities does not recognize the method 'System.Linq.IQueryable`

All I had to do was add an AsEnumerable() which converts the result into C# objects, then the select (preserving the logic I originally had) would then add the index to the iterations.

var cities = context.Countries
.Where(s => query.Name == s.Name)
.AsEnumerable()    //  where the magic happens
.Select(s => new CityDTO
{
    new CityDTO()
    {
        name = s.name,
        stateName = s.stateName
        population = s.population
    }
});