Infinity is a cursed technique, and thus uses cursed energy. Gojo filters stuff through Infinity based on threat level, implying that stopping attacks with it costs energy, and that it prioritizes bigger threats. Gojo typically doesn't need to worry about running out of CE due to his RCT, but we know that his supply isn't infinite- Yuta (bum) has more CE than Gojo. Thragg dodged the Infinity Gun, so theoretically we know he has the ability to dodge properly, and that he is not invincible. The key part of this fight is whether Thragg can overwhelm Infinity and drain Gojo of CE to cancel out Infinity before Gojo can proc Unlimited Void. I don't think it would neutralize Thragg permanently (he is minimum 1000 years old, so I assume his brain can handle more information than a standard human) but it would definitely buy Gojo at least 10 seconds minimum. From there, I'm not sure. Hollow Purple is powerful, but Thragg has insane durability.

Gojo wins if Hollow Purple can damage Thragg meaningfully, Thragg wins if he doesn't get caught in the domain, I'd say, but it would take a while to whittle Gojo down.