One solution I have been using occasionally is to check whether the value of the field/input/select differs from it's defaultValue. defaultValue would be the value that was originally in the markup, and value is the current value aka selected or entered value. This would probably differ even though the form was autopopulated.

If you want to turn off autofill altogether, it might be wise to add autocomplete="off"
on fields that are directly connected to your logic.