Tux Guitar comes to mind but some things like chord diagrams isn’t done as well as guitar pro (imo).
For chord diagrams (like at the top of GP), there’s hundreds of websites out there which show those and its probably quicker to just use those. I’ll usually just search “C chord <instrument>”.
Kind of a nothing burger.
The repo was listed as public and archived. It’s not clear from the article but I suspect that the “private” information is just a copy of what was made public and not the information added after it was made private.