Zapier and Ninox Formula Fields

If you're trying to get Ninox -> Zapier, then copy the formula script into your button as a variable to send

let x := "INSERT FORMULA CODE"

Then send it as you would any other variable.

On a separate note, if you are having troubles with Zapier i'd recommend using Make, I have both integrated in some form within my system and Make is definitely easier to use/manage

and to answer your other point

Yes you can copy a formula to a text/number field.

and to trigger the field is usually best done at the form/table level unless you are using another form field etc to trigger after some update.