One Radio Select

You need to save 1 in fv!item.notificacion in the saveInto of circle-o a!dynamicLink()

a!save(fv!item.notificacion,1)

Is there a specific reason you do not use the selection feature of that grid?

No, i try this because i see a example and i try it but i have this problem.

The expample is this community.appian.com/.../radio-button-in-grid

No, this solution do nothing

I am still not clear about the problem. Can you try pasting the code snippet here?

 /*Checkbox*/
                                        a!richTextDisplayField(
                                          value: a!richTextItem(
                                            text: {
                                              a!richTextIcon(
                                                icon: "circle-o",
                                                link: a!dynamicLink(
                                                  saveInto: {
                                                    a!save(fv!item.notificacion, 1),
                                                    a!save(
                                                      ri!contactos,
                                                      rule!ERYM_ValidarNotificacionContacto(
                                                        listaContactos: ri!contactos,
                                                        idContacto: fv!item.idContacto
                                                      )
                                                    )
                                                  },
                                                  
                                                  
                                                ),
                                                linkStyle: "STANDALONE",
                                                showWhen: or(
                                                  fv!item.notificacion = 0,
                                                  isnull(fv!item.notificacion)
                                                )
                                              ),
                                              a!richTextIcon(
                                                icon: "dot-circle-o",
                                                link: a!dynamicLink(
                                                  saveInto: {
                                                    a!save(fv!item.notificacion, 0),
                                                  }
                                                ),
                                                linkStyle: "STANDALONE",
                                                showWhen: fv!item.notificacion = 1
                                              )
                                            },
                                            size: "MEDIUM"
                                          ),
                                          
                                        ),
                                        
                                        
                                        
/*Expresion Rule*/
a!forEach(
  items: ri!listaContactos,
  expression: if(
    fv!item.idContacto <> ri!idContacto,
    a!update(ri!listaContactos.notificacion, fv!item.idContacto, 1),
    ""
  )
)

If you are trying to select only a single row then this code differs from the solution Mike gave in the above thread shared by you, change the showWhen condition accordingly.

The solution I posted there still works quite nicely   The code you've pasted here makes fundamental changes to that construct which would prevent it from working in quite the same way.  Most notably, the icon for a given row both bases its appearance on, and saves the value of, that row's identifier - not just a hardcoded "0" or "1" being saved into the row data.

I'll note that saving a value directly into the row data will probably work fine for selecting rows (like you have it), but will NOT be sufficient for making it do a "radio button" style "single select", i.e. when one row is selected, any other selected row gets de-selected, etc.  Using your approach, you'd need to have the saveInto overwrite the "1" value in any other rows while writing a "1" into the current row, for this approach to work.