Text fields are never null, that means even if you didn’t provide any value ISNULL() function takes empty as a value.
so using ISNULL() with a text field always returns false.
For example, the formula field==== IF(ISNULL(new__c) 1, 0) is always zero regardless of the value in the New field.
For text fields, use the ISBLANK function instead.
IF(ISBLANK(new__c) 1, 0) true if if has a value
IF(ISBLANK(new__c) 1, 0) false if it don’t have a value