TLDR;it could "work" if you only need position to the nearest country.
The "basics" page is worth a look.
https://www.aweigh.io/basicsI haven't looked in detail, but the premise sounds reasonable. Basically they are using the polarisation of scattered sunlight to try and determine the position of the sun. Then if you also know the time, you can calculate your location. This is basically what a sextant does.
I note that nowhere do they show the result. My guess would be that if they could make this work to within 5 to 10 degrees(lat or lon) they would be doing really well. There will be plenty of error in the polarisation measurement. An error of 1 degree would could equate to a error of 100km on the ground. And the angular diameter of the sun is about 0.5degrees to start with.
Lets not get started on the list of things that they say rely on sat positioning. Many actually use it to derive time. This project just uses a regular clock.