That would embolden the anti-trans crowd.
Unfortunately no matter the outcome there's likely danger there which is why legal protections are going to be critical. If it doesn't accurately detect trans people they'd argue it's evidence that being trans is a choice and that they could just decide to "be normal". If it does accurately detect trans people in some ways that's even more dangerous because now you've created a trans detector that could potentially be used to target people.
Ultimately from a scientific perspective there's still so much we don't know about how our brains work and even less known about how gender and sexual orientation are determined. Projects like this provide valuable clues about all of that, but there's still so much that's unknown that any result is potentially useful. I personally would find it more interesting though if it did accurately detect someone whose trans as it would suggest there's physically detectable brain differences.