I have a personal: List<Grupos> lista = new List<Grupos>();
And I have this code
var matches = lista.FindAll(x => x.Nome_Grupo.ToLower().Contains(txtFiltro.Text)).ToList();
To filter only words from my TxtFilter , I'd like to filter all items that do not have the word that I put in TxtFilter and if possible put more than one word.
Example bring all items that do not contain: pineapple, strawberry.
To filter you can use the Where method. .
var matches = lista.Where(x => !x.Nome_Grupo.ToLower().Contains(txtFiltro.Text)).ToList();
To filter more than one value you can use a List and check if the value you are filtering exists inside it.
var filtros = new List<string>() {"abacaxi", "morango"};
var matches = lista.Where(x => !filtros.Contains(x.Nome_Grupo.ToLower())).ToList();
From what I understood the question, that's it
var matches = lista.Where(x => !x.Nome_Grupo.ToLower().Contains("abacaxi") &&
!x.Nome_Grupo.ToLower().Contains("morango")).ToList();
If you need to validate many values, it would be best to put them in a collection and then validate them, thus (assuming all words are in the textbox, separated by commas - no spaces).
var palavrasFiltro = txtFiltro.Text.ToLower().Split(',');
var matches = lista.Where(x => !palavrasFiltro.Contains(x.Nome_Grupo.ToLower())).ToList();