I’ve been recommended by a smart dude something that may be even better: ESRGAN/BasicSR. It’s an AI-upscaling algorithm just like Gigapixel, but you can train it with your own datasets, so if you have a representative dataset of what you’re trying to upscale (you need high res and low res reference for training), you can get really incredible results.

I’m currently playing around with it, and while training is very slow (we’re talking many days), it’s impressive what it can do imo.