Hi @wagnerortizz ,
Does your choice column allow multiple selection?
I did a simple test with a choice column that doesn't allow multiple selections for your reference.
I put all the existing options into a collection before submitting the data, and then determine whether the current option is in the collection.
1. Here is my List.

2. Here is my App.
ClearCollect(collectionname,Distinct(AddColumns(datasource,"newcolumnname",ChoiceColumn.Value),newcolumnname));
If(Form1.Mode=FormMode.New,If(DataCardValue9.Selected.Value in collectionname,Notify("Please choose another option"),SubmitForm(Form1)),SubmitForm(Form1))

Result Screenshot:

Best Regards,
Charlie Choi