Radio Buttons and Read Only Grid

Not possible. Contrary to the editable grid, the read only grid does not support as many components.

From the documentation:

https://docs.appian.com/suite/help/23.3/Grid_Column_Component.html

The value can be text, a!imageField(), a!linkField(), a!richTextDisplayField(), a!tagField(), a!buttonArrayLayout(), a!recordActionField(), or a!progressBarField().

Why not just show the selected options in a bullet point list inside a rich text display field?

As a workaround, consider that that Read Only Grid can very easily show the Rich Text Display Field and any of its possible configurations, including all of the Rich Text Icon choices, which include various options that replicate radio buttons and checkboxes.

I need them to be able to select or unselect in case they need to.

I was thinking of doing that but since is more of a Yes or No question for the user, with Icons I dont think I can do that. In the case if they need to unselect the selected choice.

or is it possible?

Inside a read-only grid ?!?!? There is a reason for that name.

Can you provide a bit more detail as to what you're trying to allow them to select/unselect?  The concept of selection in a read-only grid is generally keyed specifically towards selection of an entire row (or set of rows), but it sounds like you might really be after something else here - I'm having a hard time telling what, though.

Is just a question of yes or no for the user, for example: are you older than 45? yes no (like the radio buttons) but for it to look "good" they want it to be inside a column of the grid, is not like the selection of the row of the grid or anything like that.

Icons in rich text fields support dynamic links that allow you to modify data ... 

If this is a yes/no question that will need to be saved into every row of an array of data, then you should probably be using an Editable Grid instead of a read-only grid.