Hi Michael, 

The modern form designer it quite different from classic designer and it does not have direct access to the document, form, fields, attributes, etc.  But you can edit the forms and fields via the LFForm Interface , you can find more information here. 

But to solve your problem, you can use a similar logic with the post you shared. You can force the calculation to update the fields when page loads by triggering a change in that field. In the following code it set the field to empty then back to its original value to trigger a "change"

I haven't test the code on specific form, but this might be a fix that you want to follow :)

var temp = LFForm.getFieldValues({fieldId: yourFieldID});

LFForm.setFieldValues({fieldId: yourFieldID}, "");

LFForm.setFieldValues({fieldId: yourFieldID}, temp );