The got you use/call from the command line is still fully open sourced afaik from when Linus made it.
The server was open sourced too afaik so that can be freely installed or run anyway by the developers (there may be ways it can be easily decentralised and run on core if the community wants to).
You are right, the core engine is opensource but Github is a propriatery web application with so many features besides being truly a hub where millions of devs are collaborating, years, "GatesHub", made me angry by applying stupid restrictions because of my nationality, an obvious act of discrimination, so I decided to do some research even started designing an alternative application based on GIT engine, documenting some ideas, planing a roadmap, stuff, but I couldn't convince a single investor to support, I'm used to reaching this point, dozens and dozens of projects with no sponsor, so, I moved on.
I'm curious tho, amid escalated regulatory threats and the way scam coin lobbyists are doing their nasty job, is it the right time for me to resume my decentralized Git application project?
"GatesHub" sound funny, BTW.