Form optional field with action to show or no-show a textfield

Hi,

I want to make a form with conditional logic.

I have two connected option fields (you can only choose one of them) and when you choose one, there is supposed to follow an action which shows a special new field in the next row.

Optional field A is selected -> a new field is shown in the next row.

Optional field B is selected -> a new (different field from optional A) field is shown in the next row.

I don't need this conditional field to be a form, it is only plane text, but I don't have the option in the form settings, to only select a textfield. It only allows me to use form fields, which doesn't work, since I don't want that people have to select the conditional field by themselves, because then I don't need the form.

Is there any solution for that problem?

thx