Hi, and welcome to the forum @baudrillard666!
A few weeks ago Grim Curio and I released a Twine game called Excalibur. We’d been working on it together for a few years, and prior to that I’d been working with another author called Duncan Bowsman.
Towards the end we built a testing page on itch and uploaded the files there, and you may well find that works better for you. For the most part we did not run into many version control problems, but we did get a few towards the end when we were hurrying to get it done in time for Spring Thing.
Of course this method meant we couldn’t both work on the file at the same time, so whichever one of us didn’t have custody of the file would work in text files that could be copied into Twine later.
This is probably not what you wanted to hear, and I’m sure there are better ways, but it worked for us, and we got there in the end!