I want to list from sqlserver a table I am using asp.net 3.1 everything I am using local attached the error and the connection

Mistake

here is my controller

I am calling these fields from the student table, but it appears to me that it is a connection problem but I have been verifying and it does not contain any errors and the connection is supposed to be fine because I can run the tables I would like you to help me solve this problem thank you very much in advance.

 [HttpGet("[action]")]
    public async Task<IEnumerable<AlumnoViewModel>> Listar()
    {
        var alumno = await _context.Alumnos.ToListAsync();

        return alumno.Select(c => new AlumnoViewModel
        {
            idalumno = c.idalumno,
            nombre = c.nombre,
            apellido = c.apellido,
            callenumero = c.callenumero,
            colonia = c.colonia,
            ciudad = c.ciudad,
            estado = c.estado,
            lada = c.lada,
            telefono = c.telefono,
            pais = c.pais,
            codigopostal = c.codigopostal,
            religion = c.religion,
            correo = c.correo,
            sexo = c.sexo,
            lugarnacimiento = c.lugarnacimiento,
            nacionalidad = c.nacionalidad,
            fechanacimiento = c.fechanacimiento,
            estadocivil = c.estadocivil,
            curp = c.curp,
            tiposangre = c.tiposangre,
            alergias = c.alergias,
            especificarenfermedad = c.especificarenfermedad,
            condicion = c.condicion,
            bautizado = c.bautizado
        });

    }

I am making my connection from appsettings.json

"ConnectionStrings": {
"Conexion": "Server=.\\DESKTOP-KB0A8AM\\SERVERSQL;Database:dbsistema;Trusted_Connection=True;MultipleActiveResultSets=true"

this is from services the injection

 services.AddControllers();
        services.AddDbContext<DbContextSistema>(options =>
        options.UseSqlServer(Configuration.GetConnectionString("Conexion")));